Меркаптоуксусная кислота

Описание

Thio glycolic acid (TGA) is the organic compound HSCH₂CO₂H . It contains both a thiol (mercaptan) and a carboxylic acid. It is a clear liquid with a strong unpleasant odor. It is readily oxidized by air to the corresponding disulfide [SCH₂CO₂H]₂.
TGA was developed in the 1940s for use as a chemical depilatory and is still used as such, especially in salt forms, including calcium thioglycolate and sodium thioglycolate. TGA is the precursor to ammonium thioglycolate that is used for permanents. TGA 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.
TGA is also used in the making of tin stabilizers often used in certain polyvinyl chloride products (such as vinyl siding).
TGA, 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 is used as nucleophile in thioglycolysis reactions used on condensed tannins to study their structure.

Химические свойства

Also known as mercaptoacetic acid, HSCH2COOH is a colorless liquid with a strong unpleasant odor. Used as a reagent for metals such as iron, molybdenum, silver, and tin,and in bacteriology.

Использование

Mercaptoacetic acid is used as a reagent formetals analysis; in the manufacture of thioglycolates, pharmaceuticals, and permanentwave solutions; and as a vinyl stabilizer.

Подготовка

Thioglycolic acid is prepared from Sodium sulfide plus Sodium monochloride acetate to yield Dithioglycollic acid. Electrolysis of the latter acid yields the title material.

Общее описание

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.

Реакции воздуха и воды

Readily oxidized by air. Water soluble.

Профиль реактивности

Mercaptoacetic acid is readily oxidized by air . Reacts readily with other oxidizing agents as well in reactions that may generate toxic gases. Incompatible with diazo and azo compounds, halocarbons, isocyanates, aldehydes, alkali metals, nitrides, hydrides, and other strong reducing agents. Reactions with these materials may generate heat and toxic and flammable gases. May react with acids to liberate hydrogen sulfide. Neutralizes bases in exothermic reactions. Reacts with cyanides, sulfites, nitrites, thiosulfates to generate flammable and toxic gases and heat. Reacts with carbonates and bicarbonates.

Опасность

Toxic by ingestion and inhalation, strong irritant to tissue, eyes, and skin.

Угроза здоровью

Mercaptoacetic acid is a highly toxic and ablistering compound. Even a 10% solutionwas lethal to most experimental animals by dermal absorption. The oral LD50 value ofundiluted acid is less than 50 mg/kg (Patty1963). The lethal dose in rabbits by skinabsorption is 300 mg/kg. The acute toxicsymptoms in test animals include weakness,respiratory distress, convulsions, irritation ofthe gastrointestinal tract, and liver damage.
Mercaptoacetic acid is a severe irritant.Contact with eyes can cause conjunctivalinflammation and corneal opacity. Skin contact can result in burns and necrosis.

Пожароопасность

Combustible material: may burn but does not ignite readily. When heated, vapors may form explosive mixtures with air: indoors, outdoors and sewers explosion hazards. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.

Профиль безопасности

Poison by ingestion, skin contact, intraperitoneal, and intravenous routes. Moderately toxic by subcutaneous route. A corrosive irritant to skin, eyes, and mucous membranes. When heated to decomposition it emits toxic fumes of SOx. See also MERCAPTANS and HYDROGEN SULFIDE.

Возможный контакт

Thioglycolic acid is used to make thioglycolates; in sensitivity tests for iron; in formulations of permanent wave solutions and depilatories; in pharmaceutical manufacture; as a stabilizer in vinyl plastics.

Канцерогенность

Thioglycolic acid was not mutagenic in a number of Salmonella typhimurium strains with or without metabolic activation.

Перевозки

UN1940 Thyoglycolic acid, Hazard class: 8; Labels: 8-Corrosive material.

Методы очистки

Mix the acid with an equal volume of *benzene; the *benzene is then distilled off to dehydrate the acid. After heating to 100o to remove most of the *benzene, the residue is distilled under vacuum and stored in sealed ampoules at 3o. [Eshelman et al. Anal Chem 22 844 1960, Beilstein 3 IV 1130.]

Несовместимости

Compounds of the carboxyl group react with all bases, both inorganic and organic (i.e., amines) releasing substantial heat, water and a salt that may be harmful. Incompatible with arsenic compounds (releases hydrogen cyanide gas), diazo compounds, dithiocarbamates, isocyanates, mercaptans, nitrides, and sulfides (releasing heat, toxic and possibly flammable gases), thiosulfates and dithionites (releasing hydrogen sulfate and oxides of sulfur). Air, strong oxidizers; bases, active metals, for example, sodium potassium, magnesium, and calcium. Readily oxidized by air. Thermal decomposition causes release of hydrogen sulfide. May attack various metals.

Утилизация отходов

Dissolve in flammable solvent and burn in furnace equipped with afterburner and alkaline scrubber.