Esterification Between Citric Acid and Callistemon citrinus, Rice-Husk, Garcinia dulcis Catalysed by Citric Acid’s-H

Esterification between citric acid molecules and molecules of Callistemon citrinus, rice husk and Garcinia dulcis (pulp-peel and pips) were carried out such as the citric acid molecules quantities (moles) were negligible against to these raw materials’ reactive molecules quantities (moles). Results showed generally an important initial, total conversions (after 60 minutes) of citric acids molecules which confirmed the essential role of raw materials’ aromatics molecules characterized by their alkene organic-function titrated with HF-0.00261N (Hydrofluoric acid) as support of citric acid’s protonic acid H + catalyst (a portion of the carboxylic acids’ citric acid molecules used), support of non-ionic citric acid’s carboxylic acid (a portion of the carboxylic acids’ citric acid molecules used) and support of raw materials molecules reagents. So, the citric acid partial order of esterification of these used raw materials (Callistemon citrinus, rice husk and Garcinia dulcis (pulp-peel and pips)) with citric acid molecules were determined. Also, the brown citric acid equivalent monomers formed during esterification were calculated and their evolution were followed for all raw materials and results allowed to determine the citric acid’s protonic acid activities. In the same time, relationship between raw materials’ external specific surfaces, estimated by calculated and measured densities, and conversion or brown citric acid equivalent formed were established to conduct finally at the catalyst turnover. The variation of alkene organic-function concentration and/or quantities not only in solution but also in all by-products allowed to an ionic mechanism of these esterification with citric acid catalyzed by citric acid’s protonic acid H + (a portion of the carboxylic acids’ citric acid molecules used) supported on all raw materials’ aromatics molecules and fiber structures in glass-flask where not only carbonic acids molecules but also hydrogens molecules gas were emitted. Finally, seeing that a non-negligible alkene organic-function quantities were titrated on all by-products, their valorization as catalytic support of citric acid molecules polymerization were carried out and a procedure constituted principally with estimation of dichloromethane and hexane insoluble/soluble products, titration with HF-0.00261N of the unsaturated organic-function in hexane soluble products and titration with NaOH-0.05N of the black citric acid equivalent quantities evolutions were established and the results confirmed the ionic mechanism of esterification with citric acid molecules during which not only carbonic gas and hydrogen gas were emitted but also new monomers and each equivalent saturated products (characterized by their globally white color and unsaturated organic-function titrated with HF-0.00261N), new polymers and poly-polymers (characterized by their globally black color and titrated with NaOH-0.05N) different to that obtained with radical mechanism catalyzed by Lewis acid sites were formed. American Journal of Applied Chemistry 2020; 8(2): 31-54 32


Introduction
The first step the characterizations of raw materials such as their compositions and also their sieving-characteristics as such as specific diameter, calculated volumetric mass (density), calculated external specific surfaces, measured density, measured external specific surfaces deduced by measured density. The second step was the esterification reaction with citric acid molecules [1] which consisted not only to esterify the acid function of the citric acid molecules by rice husk's, Garcinia dulcis' and Callistemon citrinus' organic molecules but also to esterify the acid functions of their organic molecules by the citric acid molecules' alcohol functions. Thus, citric acid polymers and esters of citric acid molecules with rice husks', Garcinia dulcis' (pips -pulp-pell) and Callistemon citrinus' organic molecules in glass-balloon auto-catalysed by citric acids' protonic acids H + were obtained with each by-products according to a mechanism. So, not only the quantifications of citric acids' protonic acid catalysts were done but also the quantification of formed esters was made by measuring out with 0.05N-NaOH solution the rest of citric acid molecules' acid functions not having been esterified [1]. Also, the quantifications of alkene-equivalent content of raw materials, esters solutions and by-products were done to evaluate their aromatics' functions on surfaces and structures contributions as catalytic support of citric acid molecules esterification, citric acid protonic acid H + -catalyst and polymerization. Finally, by-products valorization was made as catalytic support to polymerize citric acid molecules in the same time a control-procedure was established to evaluate the polymerization evolution, to confirm and established the citric acid molecules polymerization on glass-material auto-catalyzed by citric acids' protonic acid H + .

Esterification Between Citric Acid
Molecules and Organic Molecules Citric acid C 6 H 8 0 7 is a tricarboxylic acid α-hydrolyzed. It contains three acids with pKa such as pKa 1 = 3.14, pKa 2 = 4.77 and pKa 3 = 6.39 and a α-alcohol function with pKa = 14.4 [2,3,4] (Figure 1). By its reactivity, the citric acid was the object of several studies and was used in several fields like the cosmetics, the food one, the chemistry and others [5,6]. Noticed that the acid form is AH with pKa (AH). It was shown that if the pH ≤ [pKa (AH) -2], the quantity of basic Aassociated to the acid/base couple AH/Ais negligible in comparison with the AH quantity. And if the pH ≥ [pKa (AH) + 2], the quantity of acid AH associated to the acid/base couple AH/Ais negligible in comparison with the Aquantity [6]. For [pKa (AH) -2] ≤ pH ≤ [pKa (AH) + 2], the basic Aand the acid AH forms coexist but if [pKa (AH) -2] ≤ pH ≤ pKa (AH) the acid form AH dominate and if pKa (AH) ≤ pH ≤ [pKa (AH) + 2] the basic form Adominate [7]. Consequently, for the citric acid, the acids and basics forms according to the pKa and pH were showed in the following Table 1:

Esterification with Citric Acid Molecules Principles
Fischer-Speier esterification also called carboxylic acids esterification is generally a liquid phase chemical reaction between an alcohol function and a carboxylic acid function catalyzed by H + ions from acids functions on solution ( Figure  2). This reaction is accompanied with water molecules formation according to the general reaction ( Figure 3).  Thus, tricarboxylic acids of citric acid could be esterified with three alcohol functions of species' organic molecules ( Figure 4) and also species' organic molecules carboxylic acids could be esterified by the alcohol function of citric acid ( Figure 5) if the solution pH is respected [1,7] according to the general equations:  Also, tricarboxylic acids of citric acid could be in reaction with three amino-acids or amines functions of organic molecules if the solution pH is respected [1,7]   In the present manuscript, esterification between citric acid molecules and rice husk's, Garcinia dulcis' and Callistemon citrinus' organic molecules was done. The esterification experimental conditions will be described in the following paragraphs §2. 3. But above all touch on about these species' physico-chemical characteristics.

Rice Husk
Rice husk is the external part of rice grain which should be peeled mechanically or manually due to its inedible. Rice grain is made up approximatively of 17% to 23% rice husk according its variety. The constituent parts of rice husk varied according its variety, the geographic area of plantation, the season and cultivation method. But generally, rice husk is constituted of 84% to 87% of organic compounds and 13% to 16% of non-organic compound such as 12% to 13% of silica (SiO 2 ), manganese, copper, and zinc with other oxides like MgO, K 2 O, Na 2 O and CaO. Organic compounds are principally cellulose, lignin, pentosane and few quantities of proteins and vitamins. The rice saponification index is 190 and it contains approximatively 0.026 (wt/wt%) of fatty qcid, and 0.0498 (wt/wt%) of proteins [8, 9,10]. The rice husk refusals size characteristics after blinder-mix ( §2.3.2), used during experimentations, were shown in the following table 2.

Garcinia Dulcis
Garcinia dulcis is a tropical fruit tree native to Southeast Asia. Then, it was planted in Indochina, Malesia, Philippines through to New Guinea, Queensland and Australia [11,12,13]. It is also found in Africa and Madagascar such as the Garcinia dulcis used was gathered in the southeast of Madagascar at Ankaramalaza region. The scientific classification of Garcinia dulcis is shown in the following table 3 [11]. Garcinia dulcis is an evergreen tree with horizontal branches and a dense, pyramidal crown. A Garcinia dulcis fruit is composed with a green peel which is rough due to the presence of sticky liquids from its interior; a yellow fibrous-juicy pulp comestible which taste bitter-acid and pips composed with brown-husk and a buttered white cotyledon which taste bitter and spicy at the end. The refusal characteristics of Garcinia dulcis-pips after blinder-mix used during experimentations was given in the following table 4. The refusal characteristics of mixed Garcinia dulcis' pulp and peel fibrous used during experimentations was shown in the following table 5. Research on the phytochemical constituents and biological activities of Garcinia dulcis [13] have demonstrated that various parts of the plant contain an abundance of bioactive organic compounds mainly xanthones and flavonoids, with significant pharmacological properties such as anti-atherosclerosis, anti-bacterial, anti-cancer, anti-hypertension, and anti-malarial. Also, it has a long history of use as a traditional medicine for the treatment of ailments such as lymphatitis, parotitis, struma, scurvy, cough and sore throat. Garcinia dulcis contains generally 0.4 (wt/wt%) of proteins and 0.5 (wt/wt%) of lipids with only 1 (wt/wt%) of fibrous [14].

Callistemon Citrinus
Callistemon citrinus also called "bottle brush", because of its form was from Australia and New-Caledonia. Etymologically, Callistemon citrinus was from Greek "kallos"-beauty and "stêmôn" -filament. During flowering period, this bush is composed with a long etamine like a bottle-brush followed by fruits to seed capsules formations which were spherical whose peel was brown and the interior green-white delicately perfumed. Its saponification index was 202 and contains approximatively 0.3(wt/wt%) fatty acids.
The refusal characteristics of mixed Callistemon citrinus fruits-seeds capsules used during experimentations was shown in the following table 6. The scientific classification of Callistemon citrinus is shown in the following table 7 [15]. Noticed that there are about fifty (50) species of callistemon [16] but they have commonly been referred to as bottlebrushes because of their cylindrical, brush like flowers resembling a traditional bottle brush.

Equivalent-alkene Rate of Raw Materials Rice Husk, Garcinia Dulcis and Callistemon Citrinus
Equivalent-alkene (C = ) organic function rate of raw materials rice husk, Garcinia dulcis and Callistemon citrinus was measuring-out by HF-0.00261N titration according to the procedure described on the bibliography [17]. The results were showed in the following table (Table 8) such as the on surface equivalent-alkenes of raw materials was obtained at the first color variation from blue to transparent and their total equivalent-alkene was obtained at the second variation to yellow-green.
The inside-structure equivalent-alkene corresponded to alkenes of organic functions like insoluble and soluble fiber which is located and constituted the internal-structure-microstructure of each raw materials [18,19].

Esterification Between Citric Acid Molecules and Species' Organic Molecules Experimental Conditions
Three parameters were taken into account to optimize the esterification between citric acid molecules and organic molecules of rice husk -Garcinia dulcis and Callistemon citrinus such as: 1) The pH of mixed solution which were previously calculated (Table 9) [20]. Notice that all pH were less than 3.14 that is to say dominant forms were AH 3 and AH 2 -(Di-Hydrogenocitrate) ( Table 1- §2.1.). That doesn't exclude the presence of AH 2-(Mono-Hydrogenocitrate) and possibly A 3-(Citrate) when citric acid molecules located in the vicinity of basic-organic functions molecules of raw materials [1]. 2) At 60 [mn], the moles ratio between citric acid and estimated lipids or fatty acids and/or proteins of raw materials was chosen so that all the time they were around and superior to 1 to make sure that there were enough citric acid molecules for each esterification. But, for all the other times less than 60[mn], this ratio was chosen so that the lipids or fatty acids were in excess and/or in certain cases around once and maximally twice than citric acid moles (Table 9) except for Garcinia dulcis this ration was very important because the ratio-evaluation was done by taking into account of only lipids or fatty acids and proteins rate. However, noticed that for Garcinia dulcis, lipid's or fatty acids-equivalent and proteins estimated rate reflect only 0.99% (wt/wt%), in the same case for respectively Callistemon citrinus and rice husk estimated rate reflect only 30% (wt/wt%) and 2.61% (wt/wt%). Consequently, these estimated ratios were undervalued and really they should be largely inferior to zero. Also, the moles ratio between total equivalent-alkene and citric acid were deduced and showed in the following Table 9; noticed that this ratio is more than three. Finally, the weight ratio between raw material and citric acid was all the time more than three. That is to say, it's possible to consider that generally the reactive organic functions, which certainly depend on each raw material alkenes titrated, is in excess than citric acid molecules. In this case, the aim was to study the citric acid esterification kinetics and the contribution of raw materials' alkene-structure functions as catalytic support as said on the bibliography [21].
3) The mixed solution esterification temperature which were more than 373 [°K] at its ebullition temperature. Noticed that esterification was also done with pips of Garcinia dulcis and all experimental conditions were shown in the following table 9. Garcinia dulcis Catalysed by Citric Acid's-H + -Monomers and Polymers Formation Mechanism *Estimation deduced by taking account of lipids or fatty acids and proteins rate of each raw materials given by webographies. Figure 8. Raw materials' organic molecules extraction by citric acid esterification assembly.

Esterification Between Citric Acid Molecules and Species' Organic Molecules Procedure
Firstly, raw materials were mixed with a blender and their size were estimated using sieves. The refusals sizes were characterized and each mixed-raw materials characteristics were shown in the table 2, table 4, table 5 and table 6 3) respectively for rice-husk, Garcinia dulcis pips and Callistemon Citrinus. But, mixed product of Garcinia dulcis pulp-peel were so fluid with thins heterogeneous filaments and it was practically impossible to estimate their corresponding size and characteristics as sphere or cylinder. In any case, all raw materials equivalent-alkene rates were shown in table 8. Equipments accessories and chemical products used for the esterification with citric acid molecules were: balloon (250[ml]) -Liebig-condenser -heat balloon -screen -balancemagnetic stirrer -refractometer. So, secondly took and weight the citric acid and raw materials to be esterified. Prepare the citric acid solution for the esterification in the balloon and put in the raw materials. Complete the extraction assembly ( Figure 8) and finally heat the balloon inside the heat balloon at the reaction temperature. When the experimental duration has passed, stop the heat balloon without stopping the Liebig-condenser water refrigeration not only to reduce the balloon-temperature but also to eliminate the light gas leak risk. Immediately, as soon as possible change the heat balloon to a beaker containing iced-cube which not only stop the esterification-reactions but also it stop the opposite reaction -hydrolysis of the obtained esters. When the balloon temperature was carried out to room temperature, stop the refrigeration water of Liebig condenser and we obtained a homogeneous brown extracted-liquid and/or by-products (according to the experimental conditions) which was the residual of raw materials. Thus, pass the obtained solution in the balloon through the screen to recover not only the brown esters solutions of raw materials' organic molecules in a beaker which allowed to suggest a mechanism of alkene formation by citric acid molecules decarboxylation on glass flask catalyzed by its own protonic-acid-H + ( §3.) but also the by-products (retained on the screen) whose all characterizations by HF-0.00261N titration allowed to suggest a global mechanism of esterification between citric acid molecules and organic molecules -Alkene's organic molecules as heterogeneous catalytic support ( §4.) and the by-products valorization as catalytic support for citric acid polymerization §5.

Esterification Between Citric acid Molecules and Organic Molecules of Raw Materials Global Results
As described previously, the pH during esterification between citric acid and organic molecules of rice husk, Garcinia dulcis and Callistemon citrinus on glass flask were in the vicinity of 01.14 − 3.143 that is to say, on these conditions the dominant forms were AH 3 (citric acid) and AH 2 -(Di-Hydrogenocitrate) (

Citric Acid Conversions Evolution in Terms of Time (Extracts and by-Products Qualities)
According to the previous table 10, the extracted solutions colors, odors and tastes; the increasing of all by-products weight versus the initial weight of used raw materials indicates that there were not only esterification between raw materials organic functions with citric acid molecules but also polymerization of citric acid molecules occurred on raw materials' organic functions structure and/or eventually inside the porous generated by these structures [21]. Thus, the citric acid conversion increased all the time with reaction duration (Figure 9). For Garcinia dulcis pips, the citric acid conversion decrease slightly with time seeing that Garcinia dulcis contains esters of citric acid whose quantities increased with time and in the same time contributed to decrease slightly its global conversion by Na0H-0.05N titration.

Quantification of Brown Citric acid Polymers Equivalent (bp-equivalent) Formed During Esterification
Noticed that during the esterification between citric acid molecules and raw materials organic functions there was formations of not only esters but also citric acid molecules polymers such as yellow, red brick and brown citric acid polymers located on the raw materials structures and/or eventually inside its structure porosity. In these cases of experimental conditions (table 9), the polymerization of citric acids molecules were certainly catalyzed by their own protonic acid-H + seeing that any catalyst like H + /H 2 SO 4 or Fe [6,11] were used during the esterification. Thus, a mechanism of alkene formation by citric acid molecules decarboxylation on glass flask catalyzed by their own protonic acid-H + is described in the following paragraphs leading to the formations of not only citric acid polymers but also hydrogen (H 2 ) and other molecules. Also, seeing that all citric acid polymers [6] were formed during all esterification reactions, their quantifications was done by Na0H-0.05N titration and the results was given as brown citric acid polymers equivalent (bp-equivalent) which is the greatest form of polymers noticed.
Then, the decarboxylation of 2,4,7,9-tetraoxo-1,4,5,6,7,9-hexahydrooxepino[4,5-d]oxepine -5a(2H)-carboxylic acid (A) catalyzed by citric acid molecules protonic acid-H + occurred according to the mechanism described on the following figure (figure 13-decarboxylation-mechanism) with formation of carbon dioxide gas (CO 2 ), hydrogen gas (H 2 ), citric acid's protonic acid-H + catalyst regeneration and the products [ Figure  14-(B-yellow monomers)]. Hydrogenations of these B-yellow monomers obtained by glass flask catalyzed with citric acid protonic acid-H + in solution gave [ Figure 15-(D-new monomer)] and [ Figure 15-(C-new products)] according to wether respectively one or two of alkene functions were hydrogenated. Finally, B-yellow monomers polymerizations occurred also in solution catalyzed by the citric acid's protonic acid-H + according to the previous mechanism [ Figure 11(I)] to form red-brick, brown and eventually black citric acid polymers [6,20]. Noticed that in the same time, (D)-new monomers can reacted together in solution to form a new organic products-compounds without alkene functions (E) catalyzed by the citric acid's protonic acid-H + according to the previous mechanism [ Figure 11(I)] ( Figure 16). Finally, noticed that (E) could reacted together and/or reacted with another (D)-new monomers to form polymers like black citric acid polymer (F) for example ( Figure 17) and their alkene functions could be hydrogenated to form each equivalent saturated organic molecules.

Brown Citric Acid Equivalent Polymers (bp-equivalent) Quantification During esterification
According to the mechanism described Above (figure 13 decarboxylation mechanism), it was possible to quantify the carbon dioxide gas (CO 2 ) emitted during the esterification reaction. In order to ensure this, the law of mass conservation was used assuming that the water mass condensed on the assembly was counted as negligible. Then, the brown citric acid polymers equivalent (bp-equivalent) quantification during esterification was offset seeing that according to the global brown citric acid polymer formation (bp) mechanism, the moles carbon dioxide gas emitted and brown citric acid polymer ratio was 10. The following table 11 shows these results. Notice that total extracted weight was the weight of esters solution (deducted by its volume and density- Table 10) plus by-product weight (Table 10). Also, noticed that at 60[mn], the carbon dioxide conversion calculated by carbon dioxide emitted weight and citric acid with raw materials weight ratio were too high confirming not only the water molecules elimination to form alkene functions and/or esters and/or hydracids of citric acid polymers synthesized with their possible condensations on the assembly during the reactions and also the other carbon dioxide formed by raw materials' carbonic acid decarboxylation. These results confirmed also the high values of by-products increased ratio (Table 10). Assuming that all carbon dioxide emitted were from citric acid polymerization seeing that decarboxylation of raw materials' carboxylic acid functions were also possible according to the previous mechanism ( §3.2.1.), the equivalent-brown citric acid calculated.  These results confirmed that not only there were esterification between citric acid molecules and raw materials' organic functions but also polymerization between citric acid molecules and eventually decarboxylation of raw materials' carboxylic acid. Indeed, the following figures (figure 18a-18b-18c-18d) showed that the concentration of equivalent-brown citric acid polymers increased rapidly all the time for all raw materials. That allowed to study the kinetic against citric acid seeing that they were negligible in comparison with raw materials' organic molecules constituted mainly of alkenes organic functions (Table 3) and/or carboxylic acids and its derivatives in the following paragraphs on chapter 4. Also, effects of alkenes-organic molecules of raw materials as heterogeneous support contribution will be study in the following paragraph §.3.2.3.

Effects of Specific Surfaces and Initial Total Alkene Concentrations of Raw Materials During Their Esterification with Citric Acid Molecules
As shown on paragraph §3.2.1., these esterification and citric acid polymerization reactions were catalyzed in this case by citric acid's protonic acids H + which can move through raw materials' aromatics and polynuclear aromatics alkene functions [21]. So, to evaluate their contributions and activities as citric acid's protonic acids H + catalytic-support, the evolutions of citric acid conversions and brown citric acid polymers equivalent (bp-equivalent) concentrations per raw material's specific surfaces and per raw material's initial alkene concentrations were shown in the following table 12 and these figure 19 and figure 20.    These results showed clearly that initial alkenes concentrations, specific surfaces and total surfaces affected not only the initials conversion and bp-equivalent formation but also their durability along the time. Noticed that more the total surface multiplied by [C = ] initial-index of raw materials was, less will be the conversion and bp-equivalent ratio results. Noticed also that sometimes even if the time experimentation increased the conversion and bp-equivalent formation per initial alkenes concentration per total surface increased. That allowed to study the effects of citric acid's protonic acid H + and firstly calculate the initial quantities of effective citric acid's protonic acid H + which initially catalyzed reactions was done and to follow their activities and turnovers assuming that these quantities stayed stable during the experimentations seeing that the pH unregistered at 60[mn] were globally slightly higher than the initial pH. So, secondly the dispersion of citric acid's protonic acid on raw materials' aromatics and polynuclear aromatics alkene functions were calculated equals to [H + ] concentration divided by [C = ] initial concentration. Finally, the initials and the evolutions of citric acid's protonic acid H + supported on raw materials' aromatics and polynuclear aromatics alkene functions activities and turnovers were also given as shown in the following table 13.
Noticed that, for lower values of initial {total surface× [C = ] initial } index, the initial dispersions decreases when {total surface× [C = ] initial } index increases ( Figure 21). But, at a higher value of initial {total surface× [C = ] initial } index, the initial dispersion value became more important ( Figure 21).    Noticed that the initial activities and consequently the initial turnovers of citric acid's protonic acids H + for different raw materials decreased when initial dispersion increased as shown in the following figure 22 and figure 23 (Table 13). These exceptionnel results signalized the importance of alkene organic function as parameter and guided to create the « Total surface×[C = ] initial -index » (Table 13). Also, this index-value obtained by support external total surface multiplied by equivalent alkene organic-function concentration (Table 13) was calculated and it was noticed that at initial time (1') catalyst-citric acid protonic acid-H + turnovers and activities increased with this index-value except that at maximum index-value and at 60' their values go down again and confirmed the alkene-support role to improve esterification and polymerization reactions with citric acid molecules; but at 60' the formation of important PN-equivalent polymer could impinge upon catalyst-citric acid protonic acid-H + sites and their deactivations (Table 13). That is why, normally the evolution of alkene-equivalent concentration of extracts-esterified Garcinia dulcis Catalysed by Citric Acid's-H + -Monomers and Polymers Formation Mechanism products solution evolution (followed by hydrofluoric acid HF-0.00261N titration) recorded a rise at the expense generally of alkene-equivalent concentration of by-products evolution (followed by hydrofluoric acid HF-0.00261N titration) [17] at the end but as shown in the following table 14, it wasn't all the case. Effectively, the alkene concentrations of extracts-esterified product evolutions recorded a rise with time in all raw materials but in the same time alkene-equivalent concentrations of by-products increased significantly in all raw materials. These results gave notice that there were alkene formation and eventually their transformation which confirmed the synthesis of citric acid monomers and polymers asked and described on paragraph §3.2.1. through all raw materials ( Table 14). Noticed that the positive value of total alkene-equivalent formed minus total initial alkene indicates the formation of monomers and its negative values confirmed the hydrogenation (by H 2 formed during decarboxylation) of alkenes' monomers formed and /or their polymerizations to form respectively D-new monomers (figure 23), (E) (figure 24) with (C) (figure 23) and citric acid polymers as described on paragraph §3.2.1.. That is why generally alkenes formed quantities decreased with time (Table 14). In any case, all these previous results showed that citric acid molecules (with protonic acids H + or not) were initially adsorbed, dispersed and moved on the raw materials surfaces' structure by hydrogen bond. Then a part of citric acid molecules reacted with raw materials organic molecules by esterification to give raw materials citric acid esters and another parts were activated by citric acids' protonic acids H + which were supported and dispersed on alkenes' raw materials surfaces and structure by hydrogen bond to form reactive intermediates necessary to synthesize monomers and citric acid polymers according to the mechanisms described on paragraph §3.2.1.. That allowed to study and established the partial order versus citric acid concentration to understand the possible adsorption mechanism.

Esterification with Citric Acid Molecules Reaction Conditions
The first condition which permit the partial order versus citric acid of esterification with citric acid molecules reaction calculation was the concentration of citric acid must be negligible in front of raw materials molecules concentration whose verification was done in table 9 paragraph §2.3.1. seeing that reaction was done with constant volume. But to confirm this condition, seeing that there was positive proportionality correlation between initial alkene concentrations deduced by hydrofluoric acid HF-0.00261N-titration and the equivalent raw materials' reactive molecules, the following table 15 showed these initial ratios. Thus, the esterification of raw materials' reactive molecules with citric acid molecules and also citric acid molecules polymerization catalyzed by the own citric acid molecules supported on raw materials' aromatics and polynuclear alkenes global speed was: Seeing that raw materials' reactive molecules concentration was higher than citric acid concentration ( Table 9 -Table 15) the observed speed constant became 5 BA* such as 5 BA* = 5 × 38:; <:7?86:=> 8?: 764? <@=? =?>0 $ So, the global esterification and also citric acid molecules polymerization catalyzed by the own citric acids' protonic acid molecules supported on raw materials' aromatics and polynuclear alkenes, which catalyzed all reactions, on raw materials' aromatics and polynuclear alkenes (as Tanin) speed became: 4 = − 3 6786 : 6 0 7 = 5 BA* × 3 6786 : 6 0 : Studying the citric acid concentrations curve evolution with time conducted to the determination of citric acid partial order.

Citric Acid Concentrations Evolution in Terms of Time -Partial Order Determination for All Raw Materials
The following table 16 gave the evolution of citric acid concentrations. Drawing the curve 1/[citric acid] in terms of time, the following figures 16a-16b-16c-16d were obtained for all raw materials. Obtainment of straight curves involved that the resolution of the equation was possible and compatible with results experimentations only if "a" equals to "2"; in other words the esterification of raw materials' reactive molecules with citric acid molecules was order 2 against to citric acid. Consequently, from these figure 24 the observed speed constant and then the speed constant can be deduced with taking account of the previous hypothesis-conditions and the initial raw Garcinia dulcis Catalysed by Citric Acid's-H + -Monomers and Polymers Formation Mechanism materials reactive molecules concentration equals to initial total alkene concentration (Table 9-Table 12-Table 13) divided by three assuming that they are all constituted with benzene aromatics and every aromatics there were potential reactive molecules as shown the following table 17. These second order against to citric acid for all raw materials explained and confirmed not only the important initial conversion (figure 9) of citric acid molecules to reactions products as esters, monomers and polymers of citric acid but also the adsorption, desorption and move of reactants, products and citric acids' protonic acid H + catalysts molecules on raw materials' surfaces/structure aromatics and polynuclear alkenes by hydrogen bond with water.  (Table 17). To estimate the general acid constant speed and basic constant speed of the esterification of rice husk's, Garcinia dulcis pulp-peels' and Callistemon citrinus' reactive molecules with citric acid molecules and also citric acid molecules polymerization catalyzed by the own citric acid molecules supported on rice husk's, Garcinia dulcis pulp-peels' and Callistemon citrinus' aromatics and polynuclear alkenes using the values of rice husk, Garcinia dulcis pulp-peel and Callistemon citrinus and seeing that the total surface influenced the values, it was necessary to reported these values per total surface (Table 18).
Drawing the curve 5 × 3I J 0 in terms of time, the following figures 25 was obtained for these raw materials. Obtainment of straight curves gave these raw materials global acid constant speed 51 IH and basic constant speed 52 KIL (Table 18).

Valorizations of by-Products as Catalytic Support-Monomers and Polymers Formation Mechanism Confirmation
According to the previous results and mechanism, it was no doubt that after esterification with citric acids molecules ( §3.2.1.), the all raw materials by-products of esterification contained not only aromatics and polynuclear alkenes but also monomers and polymers of citric acid ( §3.2.1.). Indeed, the alkene-equivalent moles of by-products compared to initial total alkene-equivalent of raw materials (Table 19) were non negligible.
The aim of this chapter is to show that it was possible to valorize of all these by-products as another catalytic supports for another citric acid polymerizations until dry citric acid monomers; generally white sitting in the center of the glass-reactor; and citric acid polymers, brown and black according to the polymerization duration, were located nearby upside of the glass-reactor. This valorization-experimentation was done with the rice husk by-product and the evolution of these monomers and polymers quantities were followed from dry products (monomers and polymers) formation to confirm their formation-mechanism. The synthesis experimental conditions and procedure were shown in the following paragraph.

Citric Acid Polymerization Using Rice Husk by-Products Unsaturated Molecules' Organic Functions as Catalytic Support-Experimental Conditions and Results
This table 20 contained the experimental conditions such as the initial calculated-pH was as close as possible to the initial calculated-pH during rice-husk esterification and the synthesis was done in a transparent cylinder glass-bottle with a reverse glass-funnel above where gas and vapors could formed during the experimentation could evacuated little by little. According to the previous results and mechanism ( §3.2.1. - Table 14) the alkene-equivalent concentrations of extracts-esterified products solution generally increased [mol.l -1 ]. So, the first step duration of oven temperature program (388.15 [°K]) was deduced by the straight trend curve (Figure 26) between time and alkene-equivalent concentrations of extracts-esterified products solution such as the rice husk by-products total C = concentration 2.40E-2 [mol.l -1 ] became the alkene-equivalent concentrations of extracts-esterified products solution. It's only after the temperature will be increased and stabilized to 523. 15 [°K] (Table 21) until the dry citric acid monomers; generally white sitting in the center of the glass-reactor; and citric acid polymers, brown and black according to the polymerization duration were obtained.  ) to dry monomers, through dry brown citric acid polymers to black poly-polymers equivalent to polymerization of black citric acid polymers. Also, noticed that the previous evaluation of by-products valorization as another catalytic support for another citric acid polymerizations enhance to appreciate the speed transformations of monomers to polymers and poly-polymers which could index the monomers or polymers longevity evolutions. Now, the aim was to follow and to quantify each citric acid monomers evolution using hexane and dichloromethane solvent.

Hexane and Dichloromethane Soluble and Insoluble Citric Acid Monomers and Polymers Evolution Control Procedure
The first step was to quantify the total coke soluble in hexane and dichloromethane. Then, seeing that hexane was a non-polar solvent and dichloromethane a polar solvent, normally all molecules insoluble in hexane should be soluble in dichloromethane and vis-versa. However, noticed was done that the total rate of insoluble in hexane was superior to the total rate of soluble in dichloromethane. This difference confirmed the presence of (B)-yellow monomers and (D)-new monomers according to wether respectively two or one of (A)'s carboxylic acid functions were decarboxylized which were more soluble in dichloromethane according its polarity. In the otherwise, this soluble dichloromethane rate gave directly the rate of (B)-yellow monomers and (D)-new monomers with other organic compounds which contains only one alkene-function like (E) or other organic compounds with one alkene potentially soluble in dichloromethane.
Also, noticed that (B)-yellow monomers was only soluble in dichloromethane because of its conjugated-alkene but (D)-new monomers and other organic compounds which contains only one alkene-function like (E) or other organic compounds with only one alkene-function could be soluble in hexane and so constitute the majority of unsaturated molecules soluble in hexane. In that respect, to evaluate the rate of these (D)-new monomers, titration of soluble hexane (D)-new monomers and other organic compounds which contains only one alkene-function like (E) or other organic compounds with only one alkene-function with 0.00261N-HF was carried out with rectification by taking the alkene-amount of initial by-product to be valorized into consideration. Then, we can deduced firstly the rate of (B)-yellow monomers which was the most little probable monomers with two unsaturated seeing that the others conducted immediately to the formation of the most primary product PN-equivalent ( Figure 27). Also, we can deduced total weight of molecules without unsaturation which were soluble in hexane. Repeating these quantifications on each temperature-samples, the evolution of the monomers and saturated citric acid molecules by citric acid polymerization on by-products as another catalytic support will be obtained. These results were shown in the following table 23 and the figure 27. These results (Table 23, figure 27) confirmed the mechanism described on paragraph §3.2.1 such as: -(B)-yellow monomers was a primary products which could be not only hydrogenated to give (D)-new monomers but also polymerized to give black citric acid polymers PN [22] and/or PN-equivalent as shown in figure 17.
-(D)-new monomers seemed to be a primary products obtained either by only one of (A)'s carboxylic acid functions decarboxylation, either by (B)-yellow monomers hydrogenation and confirmed its transformation.
-Saturated products which were obtained by hydrogenation of (B)-yellow monomers, (D)-new monomers) and/or (D)-new monomers dismutation products to hydrogenation of (F) -polymer ( Figure 28) and confirmed its state as secondary product.
-Finally PN-equivalent molecules constituted not only with black citric acid (PN) formed by radical mechanism [6,20] but also by similar black citric acid (F)-polymer ( Figure 28) formed by ionic mechanism described previously ( Figure 17) seemed to be a primary products since 185 [mn] seeing that the hydracids functions were present and titrated by 0.05N-NaOH since the beginning of the citric acid transformation-polymerization. But, noticed that the total PN-equivalent rate decrease from 205 [mn]; so either they were transformed to black poly-polymers by hydracids-decarboxylation followed by polymerization and/or (F)-polymer polymerization (Figure 29), either their quantities increased but because of the high density of their hydrogen-bond not only on surface but also inside the rice-husk by-products structure porosity their titration by 0.05N-NaOH became difficult.

Conclusion
The previous results confirmed that raw materials' aromatics molecules and its equivalent fiber structure-porosity characterized by their alkenes organic-function titrated with hydrofluoric acid HF-0.00621N and by their estimated external specific surfaces were efficient support not only for citric acids' protonic acid-H+ catalyst but also for the reagents (citric acid and reactive molecules of raw materials Callistemon citrinus, rice husk, Garcinia dulcis pulp-peel, Garcinia dulcis pips) during the esterification with citric acid molecules and their polymerization according to the experimental conditions itemized in the manuscript. Indeed, the conversions (initial conversion at 1'; total conversion at 60') of citric acid molecules and the protonic acid-H + activities [activities], evaluated by the brown citric acid-equivalent formed per catalyst-H + dispersion, for Callistemon citrinus, rice husk, Garcinia dulcis pulp-peel, Garcinia  It was also noticed that there was relations between the support raw material characteristics "external specific surfaces" and the catalyst-citric acid protonic acid-H + activities and turnovers. Indeed, when initial dispersion increased, the catalyst-citric acid protonic acid-H + initial activities and turnovers decreased which confirmed that in all the cases citric acid molecules were initially adsorbed, dispersed and moved on aromatics' raw materials