THIOGLYCOLIC ACID

THIOGLYCOLIC ACID

Thioglycolic acid (TGA) is the organic compound HSCH2CO2H. Thioglycolic Acid is often called mercaptoacetic acid (MAA). It contains both a thiol (mercaptan) and carboxylic acid functional groups. Thioglycolic Acid is a colorless liquid with a strongly unpleasant odor. TGA is miscible with polar organic solvents.

CAS No. : 68-11-1
EC No. : 200-677-4

Synonyms:
Sulfanylacetic acid; 2-Sulfanylacetic acid; tioglikolik asit; tihoglikolic asit; thioglycolyc acid; 2-Mercaptoacetic acid; Acetyl mercaptan; Mercaptoacetate; Mercaptoacetic acid; Thioglycolic acid; Thiovanic acid; tga; mercaptoacetic acid (MAA); mercaptoacetic acid; thioglycolic acid; 68-11-1; 2-Thioglycolic acid; Acetic acid, mercapto-; Sulfanylacetic acid; 2-Mercaptoacetic acid; Thioglycollic acid; Thiovanic acid; 2-sulfanylacetic acid; Mercaptoessigsaeure; Glycolic acid, thio-; thioglycolate; Acide thioglycolique; Glycolic acid, 2-thio-; Mercaptoethanoic acid; Acetic acid, 2-mercapto-; USAF CB-35; 2-Mercaptoacetate; mercapto acetic acid; Kyselina thioglykolova; Kyselina merkaptooctova; thioglycolicacid; Thioglykolsaeure; alpha-Mercaptoacetic acid; Thioglycolic acid solution; Merkaptoessigsaeure; NSC 1894; .alpha.-Mercaptoacetic acid; Acide thioglycolique [French]; mercapto-acetic acid; UNII-7857H94KHM; Kyselina thioglykolova [Czech]; THIOGLYCOLIC ACID; CCRIS 4873; Kyselina merkaptooctova [Czech]; HSDB 2702; EINECS 200-677-4; TGA; mercaptoacetic acid (thioglycolic acid); DSSTox_CID_6141; Mercaptoacetic acid, 98%; mercaptoactic acid; 2-mercaptoaceticacid; Sulfanylacetic acid #; Thioglycolic acid, >=97%; Thioglycolic acid, >=98%; Thioglycolic acid, >=99%; 4-03-00-00600 (Beilstein Handbook Reference); Thioglycolic acid, LR, ~80%; Thioglycolic acid [UN1940] [Corrosive]; DB-002789; Thioglycolic acid [UN1940] [Corrosive]; Thioglycolic acid solution, ~70 % (w/w) in H2O; F2191-0214; Thioglycolic acid solution, ~80% in H2O, for spectrophotometric det. of palladium, iron, uranium(VI), molybdates and nitrites; mercaptoacetic acid; Thioglycolic Acid; 2-Mercapto Acetic Acid; 2-Mercapto Ethanoic Acid; Glycolic Acid, 2-thio; TGA 80%; TGA 99%

Thioglycolic Acid

Uses of Thioglycolic acid
Thioglycolic acid is used as a chemical depilatory and is still used as such, especially in salt forms, including calcium thioglycolate and sodium thioglycolate. Thioglycolic acid is the precursor to ammonium thioglycolate that is used for permanents. Thioglycolic acid and its derivatives break the disulfide bonds in the cortex of hair. One reforms these broken bonds in giving hair a "perm." Alternatively and more commonly, the process leads to depilation as is done commonly in leather processing. It is also used as an acidity indicator, manufacturing of thioglycolates, and in bacteriology for preparation of thioglycolate media. In fact thioglycolysis reactions used on condensed tannins to study their structure.

Organotin derivatives of thioglycolic acid isooctyl esters are widely used as stabilizers for PVC. These species have the formula R2Sn(SCH2CO2C8H17)2.

Applying Thioglycolic acid can soften nails and then fix pincer nails in the correct position.

Sodium thioglycolate is a component of a special bacterial growth media : thioglycolate broth. It is also used in so-called "fallout remover" or "wheel cleaner" to remove iron oxide residue from rims. Ferrous iron combines with thioglycolate to form red-violet ferric thioglycolate.

Production
Thioglycolic acid is prepared by reaction of sodium or potassium chloracetate with alkali metal hydrosulfide in aqueous medium. It can be also prepared via the Bunte salt obtained by reaction of sodium thiosulfate with chloroacetic acid:

ClCH2CO2H + Na2S2O3 → Na[O3S2CH2CO2H] + NaCl
Na[O3S2CH2CO2H] + H2O → HSCH2CO2H + NaHSO4

Reactions of Thioglycolic acid
Thioglycolic acid with a pKa of 3.83 is about 10 times stronger an acid than acetic acid (pKa 4.76):

HSCH2CO2H → HSCH2CO2− + H+
The second ionization has a pKa of 9.3:

HSCH2CO2− → −SCH2CO2− + H+
Thioglycolic acid is a reducing agent, especially at higher pH. It oxidizes to the corresponding disulfide (2-[(carboxymethyl)disulfanyl]acetic acid or dithiodiglycolic acid):

2 HSCH2CO2H + "O" → [SCH2CO2H]2 + H2O
With metal ions
Thioglycolic acid, usually as its dianion, forms complexes with metal ions. Such complexes have been used for the detection of iron, molybdenum, silver, and tin. Thioglycolic acid reacts with diethyl acetylmalonate to form acetylmercaptoacetic acid and diethyl malonate, the reducing agent in conversion of Fe(III) to Fe(II).

History of Thioglycolic acid
Scientist David R. Goddard, in the early 1930s, identified Thioglycolic acid as a useful reagent for reducing the disulfide bonds in proteins, including keratin (hair protein), while studying why protease enzymes could not easily digest hair, nails, feathers, and such. He realized that while the disulfide bonds, which stabilize proteins by cross-linking, were broken, the structures containing these proteins could be reshaped easily, and that they would retain this shape after the disulfide bonds were allowed to re-form. Thioglycolic acid was developed in the 1940s for use as a chemical depilatory.

Safety and detection of Thioglycolic acid
The LD50 (oral, rat) is 261 mg/kg, LC50 inhalation for rat is 21 mg/m3 for 4 h, and LD50 dermal for rabbit is 848 mg/kg. Mercaptoacetic acid in hair waving and depilatory products containing other mercapto acids can be identified by using thin-layer chromatography and gas chromatography. MAA also has been identified by using potentiometric titration with silver nitrate solution.

Application of Thioglycolic acid
Thioglycolic acid may be used as a sulfur source for the synthesis of metal sulfide nanostructures via hydrothermal process.

Packaging of Thioglycolic acid
100, 500 mL in glass bottle

Caution of Thioglycolic acid
At room temperature, concentrations over approximately 70% in water tend to form 1-2% thioglycolides per month, which hydrolyze to the original free compound when made acid or alkaline. The 70% solution oxidizes in air, but is stable at room temperature when tightly closed. Thioglycolate salts may also lose purity on storage. The exclusion of air does not materially improve stability.

Thioglycolic acid appears as a colorless liquid with an unpleasant odor. Density 1.325 g / cm3. Used to make permanent wave solutions and depilatories. Corrosive to metals and tissue.

radioactivity was greatest in the small intestine and kidneys of a rat that was injected i.v. with 50 mg/kg of Thioglycolic Acid. Residual 35S blood concentrations at 0.5 to 7 hours after injection did not exceed 5.3% in rats dosed with 100 mg/kg of Thioglycolic Acid. Most of the radioactivity was excreted in the urine in the form of neutral sulfate 24 hours after 100 mg/kg of Thioglycolic Acid was administered to groups of rats via i.v. and i.p. injection. Similar results were noted after rabbits received 100 and 200 mg/kg doses of Thioglycolic Acid. Significant concentrations of dithioglycolate were detected in the urine of rabbits 24 hours after Thioglycolic Acid (100-150 mg/kg) was injected i.p.

A 30% to 40% dilution of a 25.0% solution (330 mg/kg) of Thioglycolic Acid applied to dorsal skin of rabbits was excreted within 5 hours.

The distribution of radioactivity in Holtzman rats (weights 200-250 g) and in an adult New Zealand rabbit (weight not stated) after i.v. injection of Thioglycolic Acid were investigated. One rat was injected i.v. with 50 mg/kg of the test substance and killed 1 hour later. Radioactivity was greatest in the small intestine and kidneys, less in the liver and stomach, and least in the brain, heart, lungs, spleen, testes, muscle, skin, and bone. The greatest content of 35S, 0.66% of the total administered, was detected in the feces. The authors suggested that this observation may have been due to contamination of the feces with urine missed during the rinsing of urine residue from the cage after collection. The distribution of  in whole blood was evaluated in 6 rats injected i.v. with 100 mg/kg of the test substance and bled during periods of up to 7 hours. Residual  blood concentrations during 0.5 to 7 hours after injection did not exceed 5.3% in any of the 6 animals. The distribution of Thioglycolic Acid in the blood was further investigated in the New Zealand rabbit, with emphasis on binding to the following serum protein fractions: a1-, a2-, b-, and g-globulins and albumin. The test substance (70 mg/kg) was injected i.v. Most of the radioactivity was bound to albumin. The extent of this uptake amounted to 0.14% at 20 minutes after injection and had diminished to 0.016% at 3 hours. The small amount of radioactivity detected in albumin might have been due to isotopic exchange.

Small quantities of Thioglycolic Acid, as cysteine-thioglycolic acid mixed disulfide, have been identified in human urine via high-voltage paper electrophoresis.

The metabolism and excretion of Thioglycolic Acid was evaluated in male Holtzman rats (weight 200-250 g) and in adult male New Zealand rabbits (weights not stated). The test substance (100 mg/kg) was administered to 12 rats via i.v. injection and to 10 rats via intraperitoneal (i.p.) injection. Also, 2 rats were each given 75 mg/kg via i.p. injection. Animals injected i.v. (12 rats) comprised 1 group, and those injected i.p. (12 rats) comprised the other. Urine samples were collected 24 hours after injection, after which the administered  was excreted, and excretion percentages were determined. The mean urine sulfate content for i.v. dosed rats was 82.3% + 1.6% and for i.p. dosed rats was 90.6% + 1.8%. Most of the radioactivity was excreted in the form of neutral sulfate. Two rabbits were injected i.p. with 100 mg/kg of the test substance, and 1 rabbit was injected i.p. with 200 mg/kg. Urine samples were collected 24 hours after injection. The mean urine sulfur content of the 3 rabbits was 88% of the administered dose. As was true for rats, most of the radioactivity was excreted in the form of neutral sulfate. Additionally, Thioglycolic Acid (100-150 mg/kg, no radioactivity) was administered to a group of 7 rabbits via i.p. injection. Significant concentrations of dithioglycolate (average concentration 28%) were detected in the urine at 24 hr after injection. Only negligible concentrations of Thioglycolate were detected.

Thioglycolic acid (mercaptoacetic acid) is used in the manufacture of pharmaceuticals and as a vinyl stabilizer and reagent for iron. As a stabilizer for vinyl chloride plastics, and when formed from the reaction of C10-16 alkyl mercaptoacetates with dichlorodioctylstannane and trichlorooctylstannane, thioglycolic acid is safe for use as an indirect food additive.

According to the Cosmetic, Toiletry, and Fragrance Association (CTFA), Thioglycolic Acid may be prepared via the reaction of sodium or potassium chloracetate with alkali metal hydrosulfide in aqueous medium. The reaction mixture is acidified and purified by organic extraction and vacuum distillation.

Cosmetic grade Thioglycolic Acid consists of Thioglycolic Acid (78% minimum), iron (0.02 ppm maximum), and monochloroacetic acid (0.05% maximum). The following are listed in the CTFA Specification for Thioglycolic Acid: dithiodiglycolic acid (2.0% maximum), sulfated ash (0.05% maximum), arsenic (3 ppm maximum), copper (1 ppm maximum), and lead (20 ppm maximum). /Other sources/ reported that Thioglycolic Acid was pure at 99%. Water content was <0.3% and dithiodiglycolic acid, thioglycolides, and monochloroacetic acid were reported as <0.4%, <0.3%, and <100 ppm, respectively.

In widely avail commercial cold-wave prepn for waving hair there is as a rule no free thioglycolic acid. Instead these prepn contain ammonium, sodium, or calcium thioglycolate at mildly alkaline pH, commonly pH 9.5 & are far less dangerous to the eye than is free thioglycolic acid.

Thioglycolic acid is marketed as pure product or at 80-85% wt% aqueous solution.

A high pressure liquid chromatographic method is described for the determination of thioglycolic acid in hair waving fluids and depilatories. Prior to chromatography the acid is converted into a yellow-colored nitrobenzooxadioazole (NBD) derivative to permit HPLC detection at 464 nm.

Thioglycolic Acid has been identified via the following methods: potentiometric titration with silver nitrate solution, thin-layer chromatography, highpressure liquid chromatography, reversed-phase ion-pair high-performance liquid chromatography, gas chromatography, and high-performance liquid chromatography.

IDENTIFICATION AND USE: Thioglycolic acid is a clear, colorless liquid with a strong, unpleasant odor. It is used in the manufacture of pharmaceuticals, thioglycolates, permanent wave solutions, depilatories, and as a vinyl stabilizer. It is a sensitive reagent for iron, molybdenum, silver, tin. Thioglycolic acid is also used as a hair waving agent. In addition it is used in hydraulic fracturing mixtures to prevent precipitation of metal oxides (iron control). 

HUMAN EXPOSURE AND TOXICITY: An eczematous rash of the scalp, face & hands often results from contact with the thioglycolate of "cold wave" material used by hairdressers. This material has been reported to be absorbed in sufficient quantity to cause death. A lotion base containing 4.5% Thioglycolic Acid was applied to a 2 x 2-cm area of patients. Sites were rinsed 10 minutes later. None of the subjects had signs of inflammation. After a 12-hour interval, the lotion was applied to pubic, perineal, and scrotal regions, and sites were rinsed 10 minutes later. The lotion was not irritating to majority of the patients. Some patients complained of a hot sensation around the scrotum that lasted for only a few minutes. Thioglycolic acid (TGA) is the active ingredient of permanent-waving solution (PWS). The effect of TGA-containing PWS on the health of a human population was evaluated in 3 substudies. Firstly, 57 female hairdressers exposed to TGA-containing PWS (cases) and 64 female schoolteachers (controls) were studied. Their menstruation state was evaluated with information obtained from interviews. The results revealed that the menoxenia rate in the cases was significantly higher than that in the controls. Secondly, 8 female hairdressers selected from those that participated in the above survey underwent a fluctuation test for the mutagenic activity of urine. Eight female medical students were chosen as controls. Difference in the mutagenic activity of urine on S. tiphymurium TA100 between the two groups was highly significant. Finally, a micronucleus assay was carried out on scalp hair follicle cells in healthy volunteers. Scalp hair with the follicle cell mass was sampled from 8 male and 8 female volunteers before permanent waving and at 24, 48 and 72 hr after waving. One thousand hair follicle cells were examined by light microscopy. The number of cells containing a micronucleus and the number of micronuclei in each cell was determined. The permillages of micronuclei in hair follicle cells before and after permanent waving were compared. Micronuclei presence reached its peak value 24 hr after permanent waving, which was significantly higher than that before waving. The rate decreased progressively after 24 hr. Thioglycolic acid was tested at concentrations of up to 300 ug/mL without metabolic activation and of up to 1000 ug/mL with metabolic activation in an in vitro chromosome aberration test in human lymphocytes. Exposures were for 24 and 48 hours in absence of S9-mix and 2 hours in presence of S9-mix. Cytotoxicity was observed at a concentration of 300 ug/plate without S9-mix and at and above 1000 ug/mL with S9-mix. Thioglycolic acid did not induce a biological relevant increase in the number of cells with structural chromosome aberrations compared to the untreated controls in this test. Small quantities of Thioglycolic Acid, as cysteine-thioglycolic acid mixed disulfide, have been identified in human urine via high-voltage paper electrophoresis. 

ANIMAL STUDIES: Thioglycolic Acid (5%) caused death in a monkey at a dose of 300 mg/kg. Rats receiving the 660 mg/kg dose of Thioglycolic acid dermally died within 24 hours, whereas none of the animals in the 330 mg/kg dose group died. The following effects of Thioglycolic acid have been reported: potentiation of bradykinin-induced contractions of guinea pig gut and uterus; inactivation of hypocalcemic activity of the salivary gland hormone, b-parotin; stimulation of guinea pig skin histidase activity; inhibition of thyroid iodinating enzyme system (in calf thyroid) in the presence of a hydrogen peroxide-generating system; inhibition of uterine response to oxytocin in rats; diabetogenic effect in rats; reduction of rat hepatic succinoxidase activity; reduction of bovine antidiuretic factor activity; and inhibition of fatty acid oxidation. The effects of Thioglycolic acid on oocyte maturation and in vitro fertilization (IVF) in mice were studied by the method in vitro culture and IVF in mice oocyte. Results: The results showed that Thioglycolic acid could inhibit the germinal vesicle breakdown (GVBD) of mouse oocyte in vitro culture, but had no impact on GVBD in vivo. Thioglycolic acid could also inhibit the extruding of first polar baby and affect the quality and viability of mouse oocytes and reduce the fertilization rate of IVF and the oocytes number which were stimulated through superovulation. Thioglycolic acid might be hazardous to the meiotic maturation of mouse oocyte and might reduce the fertility of oocyte. That meant Thioglycolic acid had a reproductive toxicity to female mice to some extent. Thioglycolic acid was not mutagenic using S. typhimurium strains TA 1535, TA 1537, and TA 1538 with or without metabolic activation. A sex-linked recessive lethal mutation test was used in Drosophila melanogaster to evaluate the mutagenic potential of Thioglycolic Acid. The test solution was not mutagenic to any of the 309 X chromosomes tested. In vivo micronucleus testing of Thioglycolic Acid has been completed in the mouse, by oral and dermal routes of administration and no genotoxicity was found. Significant concentrations of dithioglycolate were detected in the urine of rats at 24 hr after injection. Only negligible concentrations of Thioglycolate were detected.

A Thioglycolic Acid (4.5% wt/wt with pH of 12-12.5) containing spray or lotion was used for preoperative preparation of the scrotum and perineum of 45 patients. Of these, 33 patients had no irritation and 11 noted a ''hot'' feeling. Twenty-six patients had previously undergone the preoperative razor shaving and 85% of the patients preferred the Thioglycolic Acid containing preparations. Four patients did not prefer the Thioglycolic Acid containing preparations because they felt it was ''messy.'' Four patients had hair-bearing skin inlay urethroplasty (hair in the urethra) and placed Thioglycolic Acid containing preparations in the urethra for 10 to 30 minutes. These patients reported discomfort on voiding the bladder that lasted for 24 hours and caused some edema of mucosa in the navicular fossa. However, all evidence of discomfort disappeared by 36 hours and there were no systemic or late complication reactions reported.

Acute Exposure/ Male rats that inhaled 620 ppm (at room temperature) or 8200 ppm (heated to 125 °C) thioglycolic acid for 7 hr showed no untoward effect during the exposure or during a 2-wk post exposure observation period.

Acute Exposure/ CdTe quantum dots (QDs) are nanocrystals of unique composition and properties that have found many new commercial applications; ... The lab study was performed to determine the developmental and behavioral toxicities to zebrafish under continuous exposure to low concentrations of CdTe QDs (1-400 nM) coated with thioglycolic acid (TGA). The results show: the 120 hr LC(50) of 185.9 nM, the lower hatch rate and body length, more malformations, and less heart beat and swimming speed of the exposed zebrafish, the brief burst and a higher basal swimming rate of the exposed zebrafish larvae during a rapid transition from light-to-dark, and the vascular hyperplasia, vascular bifurcation, vascular crossing and turbulence of the exposed FLI-1 transgenic zebrafish larvae. /CdTe quantum dots coated with thioglycolic acid.

Thioglycolic acid's production and use as a chemical intermediate, as an ingredient in hair waving solutions and depilatories, and vinyl stabilizer may result in its release to the environment through various waste streams. Its use in hydraulic fracturing will result in its direct release to the environment. If released to air, a vapor pressure of 8.68X10-2 mm Hg at 25 °C indicates Thioglycolic acid will exist solely as a vapor in the atmosphere. Vapor-phase Thioglycolic acid will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 10 hrs. Thioglycolic acid does not contain chromophores that absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight. If released to soil, Thioglycolic acid is expected to have very high mobility based upon an estimated Koc of 1.4. The pKa of Thioglycolic acid is 3.55, indicating that this compound will exist almost entirely in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts. Volatilization from moist soil is not expected because the compound exists as an anion and anions do not volatilize. Thioglycolic acid is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Utilizing the Japanese MITI test, 100% of the Theoretical BOD was reached in 4 weeks indicating that biodegradation is an important environmental fate process in soil and water. If released into water, Thioglycolic acid is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. The pKa indicates Thioglycolic acid will exist almost entirely in the anion form at pH values of 5 to 9 and, therefore, volatilization from water surfaces and bioconcentration are not expected to be an important fate processes. Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions (pH 5 to 9). Occupational exposure to Thioglycolic acid may occur through inhalation of aerosols and dermal contact with this compound at workplaces where Thioglycolic acid is produced or used. Use data indicate that the general population may be exposed to Thioglycolic acid via inhalation of aerosols and dermal contact with consumer products containing Thioglycolic acid. 

Based on a classification scheme, an estimated Koc value of 1.4, determined from a structure estimation method, indicates that Thioglycolic acid is expected to have very high mobility in soil. The pKa of Thioglycolic acid is 3.55, indicating that this compound will exist almost entirely in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts. Volatilization from moist soil is not expected because the compound exists as an anion and anions do not volatilize. Thioglycolic acid is not expected to volatilize from dry soil surfaces based upon a vapor pressure of 8.68X10-2 mm Hg at 25 °C. Utilizing the Japanese MITI test, 100% of the Theoretical BOD was reached in 4 weeks indicating that biodegradation is an important environmental fate process in soil.

According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere, Thioglycolic acid, which has a vapor pressure of 8.68X10-2 mm Hg at 25 °C, is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase Thioglycolic acid is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 10 hrs, calculated from its rate constant of 3.8X10-11 cu cm/molecule-sec at 25 °C that was derived using a structure estimation method. Thioglycolic acid does not contain chromophores that absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight.

Thioglycolic acid, present at 100 mg/L, reached 100% of its theoretical BOD in 4 weeks using an activated sludge inoculum at 30 mg/L in the Japanese MITI. After 34 days acclimation in a laboratory model river inoculated with synthetic wastewater, Thioglycolic acid was observed to biodegrade following sequencing stages of adaptation. Closed Bottle tests using an activated sludge seed indicated 67% biodegradation of Thioglycolic acid after 28 days. In 7 aerobic Closed Bottle screening tests using sewage and soil as inoculum, none reached the pass level of >60% BODT after 28 days; in 16 OECD screening tests 13% of the tests reached the pass level of >70% DOC following 28 days incubation in a sewage and soil inoculum; in 2 sets of aerobic Japanese MITI screening tests using activated sludge seeds, 6 out of 10 and 4 out of 10 reached the pass level of >60% BODT after 14 days incubation; in five Sturm CO2 Evolution screening tests using a sewage seed, 60% reached the pass level of >60% CO2; and in six Zahn-Wellens screening tests using an activated sludge seed 67% reached the pass level of >70% DOC removal. Thioglycolic acid was categorized as intermediate in biodegradability following respirometric tests using an activated sludge seed.

The rate constant for the vapor-phase reaction of Thioglycolic acid with photochemically-produced hydroxyl radicals has been estimated as 3.8X10-11 cu cm/molecule-sec at 25 °C using a structure estimation method. This corresponds to an atmospheric half-life of about 10 hours at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm. Aqueous hydroxyl radical rate constants of 9X10+8, 3.6X10+9 and 6X10+9 L/mol-sec were determined for Thioglycolic acid at pH 1(2-4); these values correspond to half-lives of 2.4 years, 220 and 130 days, respectively, at an aqueous hydroxyl radical concentration 1X10-17 mol/L. Thioglycolic acid is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions. Thioglycolic acid does not contain chromophores that absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight.

Using a structure estimation method based on molecular connectivity indices, the Koc of Thioglycolic acid can be estimated to be 1.4. According to a classification scheme, this estimated Koc value suggests that Thioglycolic acid is expected to have very high mobility in soil. The pKa of Thioglycolic acid is 3.55, indicating that this compound will exist almost entirely in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts.

A pKa of 3.55 indicates Thioglycolic acid will exist almost entirely in the anion form at pH values of 5 to 9 and, therefore, volatilization from water surfaces is not expected to be an important fate process. Thioglycolic acid is not expected to volatilize from dry soil surfaces based upon a vapor pressure of 8.68X10-2 mm Hg.

NIOSH (NOES Survey 1981-1983) has statistically estimated that 30,055 workers (15,141 of these were female) were potentially exposed to Thioglycolic acid in the US. Occupational exposure to Thioglycolic acid may occur through inhalation of aerosols and dermal contact with this compound at workplaces where Thioglycolic acid is produced or used. Use data indicate that the general population may be exposed to Thioglycolic acid via inhalation of aerosols and dermal contact with consumer products containing Thioglycolic acid.

Product overview
Thioglycolic acid (TGA or mercaptoacetic acid, CAS 68-11-1) is a high-performance chemical containing mercaptan and carboxylic acid functionalities. 
Thioglycolic acid is completely miscible in water and is used in industries and applications as diverse as oil and gas, cosmetics, cleaning, leather processing, metals, fine chemistry and polymerization. Thioglycolic acid forms powerful complexes with metals that give it specific characteristics sought after for the assisted recovery of ore as well as for cleaning and corrosion inhibition.

Key Benefits of Thioglycolic acid
At temperatures above 70°C – common temperatures in well bores, Thioglycolic acid is more efficient than classic ferric ion chelating agents (citric acid, acetic acid, EDTA, NTA). Moreover, TGA is more efficient than classic ferric reducing agents, such as erythorbic acid or ascorbic acid.

Thioglycolic acid reduces Fe3+ (ferric) ions to chelated Fe2+ (ferrous) ions that remain in solution at pH < 7.5
Thioglycolic acid is stable and efficient at low pH (TGA rapidly reduces high quantities of Fe3+)
Thioglycolic acid can control very high concentrations of ferric iron - up to about 10%.

Industry applications
Due to its mercaptan functional group, thioglycolic acid and its salts provide essential properties in a wide range of applications.

Petrochemical
The bronsted acid characteristics of thioglycolic acid and its thiol functionality make it a chemical of choice for the preparation or regeneration of metal catalysts for hydrodesulfurization.

Metals recovery
Thioglycolic acid derivatives are also used as depressants in flotation processes for separating valuable metals from ores in mining operations. Thioglycolic acid derivatives are a safer alternative to the more traditional sodium sulfhydrate (NaSH), particularly in mining environments.

Polymerization
Thioglycolic acid is a very effective chain transfer agent for emulsion polymerizations in aqueous media, in particular for acrylic acid and acrylates. The total miscibility of Thioglycolic acid with water is a benefit in this application.

Cosmetics
The salts of thioglycolic acid and also some of its esters are used in the formulation of perms and for the preparation of depilatory creams. In these applications, the main salts are ammonium thioglycolate and potassium thioglycolate. In some areas, glycerol monothioglycolate is also used.

Cleaning formulations
Due to their ability to complex with metals, thioglycolic acid and thioglycolic acid salts are excellent additives in cleaning solutions, in particular for automotive applications including automotive wheel rim cleaners.

Leather processing
Alkaline sodium thioglycolate is used in removal of hair from leather hides. It minimizes wastewater treatment costs as compared to the more toxic and harmful sodium hydrosulfide.

Fine chemicals
Thioglycolic acid is used for the preparation of pesticides such as thifensulfuron herbicide, or for polythiols or thio-esters.

Petroleum refining
In the catalytic cracking of hydrocarbons for petroleum refining, mercaptides of thioglycolic acid are effectively used as a heavy metal passivator that counteracts the adverse effects of metal (Ni, V, Fe) contaminants on catalysts.