Citric acid, decomposition

Theoretical studies [21, 22] have postulated that emergence of autotrophic metabolic pathways, such as reductive citric acid cycle (RCC) may have occurred under high P-T hydrothermal conditions analogous to deep marine hydrothermal vents. Earlier experimental work established that citric acid decomposition under hydrothermal conditions leads to the... 

This fact may be understood as a result of deprotonation of the hydroxy groups of citric acid when the initial step of citric acid decomposition—water elimination— becomes impossible. Indeed, Narendar (1997) found that decomposition temperature ofPbCA2 is about 100°C lower than decomposition temperature of the Pb2CA2 when the -OH groups are deprotonated. 

In appHcations as hard surface cleaners of stainless steel boilers and process equipment, glycoHc acid and formic acid mixtures are particularly advantageous because of effective removal of operational and preoperational deposits, absence of chlorides, low corrosion, freedom from organic Hon precipitations, economy, and volatile decomposition products. Ammoniated glycoHc acid Hi mixture with citric acid shows exceUent dissolution of the oxides and salts and the corrosion rates are low. 

Complexing agents, which act as buffers to help control the pH and maintain control over the free metal—salt ions available to the solution and hence the ion concentration, include citric acid, sodium citrate, and sodium acetate potassium tartrate ammonium chloride. Stabilizers, which act as catalytic inhibitors that retard the spontaneous decomposition of the bath, include fluoride compounds thiourea, sodium cyanide, and urea. Stabilizers are typically not present in amounts exceeding 10 ppm. The pH of the bath is adjusted. 

Decomposition. When heated above 175°C, citric acid decomposes to form aconitic acid [499-12-7] citraconic acid [498-25-7], itaconic acid [97-65 ], acetonedicarboxyhc acid [542-05-2], carbon dioxide, and water, as shown in Figure 1. 

Fig. 1. Thermal decomposition of citric acid (1) to aconitric acid (2), citraconic acid (3), itaconic acid (4), and oxidation to acetonedicarboxylic acid (5).

Salt Formation. Citric acid forms mono-, di-, and tribasic salts with many cations such as alkahes, ammonia, and amines. Salts may be prepared by direct neutralization of a solution of citric acid in water using the appropriate base, or by double decomposition using a citrate salt and a soluble metal salt. 

Cosmetics and Toiletries. Citric acid and bicarbonate are used in effervescent type denture cleansers to provide agitation by reacting to form carbon dioxide gas. Citric acid is added to cosmetic formulations to adjust the pH, act as a buffer, and chelate metal ions preventing formulation discoloration and decomposition (213—218). 

It should be emphasized that citric acid is not the only possible acid employed in Pechini-type syntheses. Other polybasic carboxylic hydroxy acids (malic, tartaric, hydroxyglutaric, etc.) and polybasic carboxylic acids (e.g., succinic) have been probed in Refs. [4, 13-16], As far as amino acids are concerned, glycine seems to remain the only representative [13, 14]. However, the choice of each particular organic acid has never been justified, and no comparative studies are performed in order to find possible dependencies of the process (ability to form a sol, a gel, or a resin, easiness of thermal decomposition of precursors, etc.) on the steric factors, specifically, on the number of hydroxy and carboxylic groups in the molecule of an acid, as well as on the length of its carbon skeleton. 

See also Acetoacetyl-CoA in citric acid cycle, 6 633 Acetyl cyclohexanesulfonyl peroxide (ACSP), 74 282 78 478 Acetylene(s), 7 177-227, 227-228 25 633 addition of hydrogen chloride to, 73 821 from calcium carbide, 4 532, 548 carbometalation of, 25 117 as catalyst poison, 5 257t chemicals derived from, 7 227-265 decomposition of, 70 614 Diels-Alder adduct from cyclopentadiene, 8 222t direct polymerization, 7 514 economic aspects of, 7 216-217 explosive behavior of, 7 181-187 as fuel, 7 221-222 health and safety factors related to, 7 219... 

Chen et al. (1997a) analysed sodium saccharin in soft drinks, orange juice and lemon tea after filtration by injection into an ion-exclusion column with detection at 202 nm. Recoveries of 98-104% were obtained. They reported that common organic acids like citric and malic and other sweeteners did not interfere. Qu et al. (1999) determined aspartame in fruit juices, after degassing and dilution in water, by IC-PAD. The decomposition products of aspartame, aspartic acid and phenylanaline were separated and other sweeteners did not interfere. The recoveries of added aspartame were 77-94%. Chen et al. (1997b) separated and determined four artificial sweeteners and citric acid. 

Acetone dicarboxylic acid was first obtained by the action of concentrated sulfuric acid upon citric acid.1 It has been made also by the gradual decomposition of a mixture of lime and sucrose.2 The most satisfactory method, however, for producing this substance, is by the action of fuming sulfuric acid upon citric acid. Details of this preparation have been modified a number of times with the intention of improving the yield.3... 

Malic and citric acids have been adequately identified from molasses as their crystalline hydrazides.119 It is probable that at least the former is a normal juice constituent. Lactic acid was identified as its zinc salt in molasses119 it arises from bacterial action. Formic acid is present119 it probably has an origin, at least in part, in sugar decomposition. Acetic and propionic acids are components and their amounts serve as a rough index of the activity of the microorganisms introduced into the molasses. The microbial count of cane juice, molasses and related products has been determined (Table IV).190... 

The melting points of the various benzimidazoles (see Table I) cover a considerable range of temperatures, and with the specific rotations as observed in N hydrochloric acid or 5 % aqueous citric acid (see Table I) will serve to characterize new and identify known benzimidazoles from aldonic acids. While the substances usually melt with decomposition, the values are readily reproducible. The rotations will be discussed further in the final section of this review. 

Aconitic Acid occurs in the leaves and tubers of Aconitum napellus L. (Fam. Ranunculaceae) and various species of Achillea and Equisetum, in beet root, and in sugar cane. It may be synthesized by the dehydration of citric acid by sulfuric or methanesulfonic acid. Aconitic Acid from the above sources has the trans configuration. It has a melting point of 195° to 200° with decomposition. It is practically odorless and has a winy taste. It is soluble in water and in alcohol and is slightly soluble in ether. 

Readily Carbonizable Substances Transfer 1.00 + 0.01 g of finely powdered Citric Acid to a 150-mm x 18-mm (od) tube previously rinsed with 10 mL of 98% sulfuric acid at 90° or used exclusively for this test. Add 10 + 0.1 mL of 98% sulfuric acid, carefully agitate the tube until solution is complete, and immerse the tube in a water bath at 90° + 1° for 1 h. Occasionally remove the tube from the water bath and carefully agitate it to ensure that the Citric Acid is dissolved and gaseous decomposition products are allowed to escape to the atmosphere. Cool the tube to ambient temperature, carefully shake the tube to ensure that all gases are removed, and using an adequate spectrophotometer, measure the absorbance and transmission of the solution at 470 nm in a 1-cm cell. The absorbance does not exceed 0.52, and the transmission is equal to or exceeds 30%. 

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