Category:Alpha hydroxy acids
Pages in category "Alpha hydroxy acids"
The following 28 pages are in this category, out of 28 total. This list may not reflect recent changes (learn more).
The following 28 pages are in this category, out of 28 total. This list may not reflect recent changes (learn more).
1. Citric acid – Citric acid is a weak organic tricarboxylic acid having the chemical formula C6H8O7. It occurs naturally in citrus fruits, in biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. More than a million tons of acid are manufactured every year. It is used widely as an acidifier, as a flavoring and chelating agent, a citrate is a derivative of citric acid, that is, the salts, esters, and the polyatomic anion found in solution. An example of the former, a salt is trisodium citrate, when part of a salt, the formula of the citrate ion is written as C6H5O73− or C3H5O33−. Citric acid exists in greater than trace amounts in a variety of fruits and vegetables, lemons and limes have particularly high concentrations of the acid, it can constitute as much as 8% of the dry weight of these fruits. The concentrations of acid in citrus fruits range from 0.005 mol/L for oranges and grapefruits to 0.30 mol/L in lemons. Within species, these values vary depending on the cultivar and the circumstances in which the fruit was grown, wehmer discovered Penicillium mold could produce citric acid from sugar. However, microbial production of citric acid did not become important until World War I disrupted Italian citrus exports. In this production technique, which is still the major route to citric acid used today. The source of sugar is corn steep liquor, molasses, hydrolyzed corn starch or other inexpensive sugary solutions, in 1977, a patent was granted to Lever Brothers for the chemical synthesis of citric acid starting either from aconitic or isocitrate/alloisocitrate calcium salts under high pressure conditions. This produced citric acid in near quantitative conversion under what appeared to be a reverse non-enzymatic Krebs cycle reaction, in 2007, worldwide annual production stood at approximately 1,600,000 tons. More than 50% of this volume was produced in China, citric acid was first isolated in 1784 by the chemist Carl Wilhelm Scheele, who crystallized it from lemon juice. It can exist either in a form or as a monohydrate. The anhydrous form crystallizes from hot water, while the forms when citric acid is crystallized from cold water. The monohydrate can be converted to the form at about 78 °C. Citric acid also dissolves in ethanol at 15 °C. It decomposes with loss of carbon dioxide above about 175 °C, citric acid is normally considered to be a tribasic acid, with pKa values, extrapolated to zero ionic strength, of 5.21,4.28 and 2.92 at 25 °C
2. Malic acid – Malic acid is an organic compound with the molecular formula C4H6O5. It is an acid that is made by all living organisms, contributes to the pleasantly sour taste of fruits. Malic acid has two forms, though only the L-isomer exists naturally. The salts and esters of malic acid are known as malates, the malate anion is an intermediate in the citric acid cycle. L-Malic acid is the naturally occurring form, whereas a mixture of L-, malate plays an important role in biochemistry. In the C4 carbon fixation process, malate is a source of CO2 in the Calvin cycle, in the citric acid cycle, -malate is an intermediate, formed by the addition of an -OH group on the si face of fumarate. It can also be formed from pyruvate via anaplerotic reactions, malate is also synthesized by the carboxylation of phosphoenolpyruvate in the guard cells of plant leaves. Malate, as an anion, often accompanies potassium cations during the uptake of solutes into the guard cells in order to maintain electrical balance in the cell. The accumulation of these solutes within the cell decreases the solute potential, allowing water to enter the cell. Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785, antoine Lavoisier in 1787 proposed the name acide malique, which is derived from the Latin word for apple, mālum—as is its genus name Malus. In German it is named Äpfelsäure after plural or singular of the fruit apple, Malic acid contributes to the sourness of green apples. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/l and it confers a tart taste to wine, although the amount decreases with increasing fruit ripeness. The taste of malic acid is very clear and pure in rhubarb and it is also a component of some artificial vinegar flavors, such as salt and vinegar flavored potato chips. The process of malolactic fermentation converts malic acid to much milder lactic acid, Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism. Malic acid, when added to products, is denoted by E number E296. Malic acid is the source of extreme tartness in United States-produced confectionery and it is also used with or in place of the less sour citric acid in sour sweets. These sweets are sometimes labeled with a warning stating that excessive consumption can cause irritation of the mouth and it is approved for use as a food additive in the EU, US and Australia and New Zealand. Malic acid provides 10 kJ of energy per gram during digestion, racemic malic acid is produced industrially by the double hydration of maleic anhydride
3. Lactic acid – Lactic acid is an organic compound with the formula CH3CHCO2H. In its solid state, it is white and water-soluble, in its liquid state, it is clear. It is produced naturally and synthetically. With a hydroxyl group adjacent to the group, lactic acid is classified as an alpha-hydroxy acid. In the form of its base called lactate, it plays a role in several biochemical processes. In solution, it can ionize a proton from the carboxyl group, compared to acetic acid, its pKa is 1 unit less, meaning lactic acid deprotonates ten times more easily than acetic acid does. This higher acidity is the consequence of the hydrogen bonding between the α-hydroxyl and the carboxylate group. Lactic acid is chiral, consisting of two optical isomers, one is known as L--lactic acid or -lactic acid and the other, its mirror image, is D--lactic acid or -lactic acid. A mixture of the two in equal amounts is called DL-lactic acid, or racemic lactic acid, DL-lactic acid is miscible with water and with ethanol above its melting point which is around 17 or 18 °C. D-lactic acid and L-lactic acid have a melting point. In animals, L-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase in a process of fermentation during normal metabolism and exercise. The concentration of lactate is usually 1–2 mmol/L at rest. In industry, lactic acid fermentation is performed by lactic acid bacteria and these bacteria can also grow in the mouth, the acid they produce is responsible for the tooth decay known as caries. In medicine, lactate is one of the components of lactated Ringers solution. These intravenous fluids consist of sodium and potassium cations along with lactate and chloride anions in solution with distilled water and it is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burns. Lactic acid was isolated for the first time by the Swedish chemist Carl Wilhelm Scheele in 1780 from sour milk, the name reflects the lact- combining form derived from the Latin word for milk. In 1808, Jöns Jacob Berzelius discovered that lactic acid also is produced in muscles during exertion and its structure was established by Johannes Wislicenus in 1873. In 1856, Louis Pasteur discovered Lactobacillus and its role in the making of lactic acid, lactic acid started to be produced commercially by the German pharmacy Boehringer Ingelheim in 1895
4. Mandelic acid – Mandelic acid is an aromatic alpha hydroxy acid with the molecular formula C6H5CHCO2H. It is a crystalline solid that is soluble in water. It is a precursor to various drugs. The racemic mixture is known as paramandelic acid, mandelic acid was discovered in 1831 by the German pharmacist Ferdinand Ludwig Winckler while heating amygdalin, an extract of bitter almonds, with diluted hydrochloric acid. The name is derived from the German Mandel for almond, derivatives of mandelic acid are formed as a result of metabolism of adrenaline and noradrenaline by monoamine oxidase and catechol-O-methyl transferase. Mandelic acid is prepared by the acid-catalysed hydrolysis of mandelonitrile. It also arises by heating phenylglyoxal with alkalis and it arises from the biodegradation of styrene, as detected in urine. Mandelic acid has a history of use in the medical community as an antibacterial. It has also used as an oral antibiotic, and as a component of chemical face peels. The drugs cyclandelate and homatropine are esters of mandelic acid, pemoline is synthesized by the condensation of the ethyl ester of mandelic acid with guanidine. Amolanone This article incorporates text from a now in the public domain, Chisholm, Hugh
5. Homocitric acid – Homocitric acid is an organic compound with the formula HOC. This tricarboxylic acid occurs naturally as a component of the cofactor of certain nitrogenase proteins. Biochemists often refer to this cofactor as homocitrate, which is the bases that predominate in neutral aqueous solutions of this species. The molecule is related to citric acid by the addition of one methylene unit, unlike citric acid, homocitric acid is chiral. The acid exists in equilibrium with the lactone
6. Glycolic acid – Glycolic acid, chemical formula C2H4O3, is the smallest α-hydroxy acid. This colorless, odorless, and hygroscopic crystalline solid is soluble in water. It is used in various skin-care products, glycolic acid is found in some sugar-crops. A glycolate or glycollate is a salt or ester of glycolic acid, the name glycolic acid was coined in 1848 by French chemist Auguste Laurent. He proposed that the amino acid glycine — which was then called glycocolle — might be the amine of a hypothetical acid, glycolic acid was first prepared in 1851 by German chemist Adolph Strecker and Russian chemist Nikolai Nikolaevich Sokolov. They produced it by a treating hippuric acid with nitric acid and nitrogen dioxide to form an ester of benzoic acid and glycolic acid and they boiled the ester for days with dilute sulfuric acid, thereby obtaining benzoic acid and glycolic acid. Glycolic acid can be synthesized in various ways, the predominant approaches uses a catalyzed reaction of formaldehyde with synthesis gas, for its low cost. It is also prepared by the reaction of chloroacetic acid with sodium hydroxide followed by re-acidification, other methods, not noticeably in use, include hydrogenation of oxalic acid, andhydrolysis of the cyanohydrin derived from formaldehyde. Some of todays glycolic acids are formic acid-free, glycolic acid can be isolated from natural sources, such as sugarcane, sugar beets, pineapple, cantaloupe and unripe grapes. Glycolic acid can also be prepared using an enzymatic process that may require less energy. Glycolic acid is used in the industry as a dyeing and tanning agent, in food processing as a flavoring agent and as a preservative. It is also used in adhesives and plastics, glycolic acid is often included into emulsion polymers, solvents and additives for ink and paint in order to improve flow properties and impart gloss. It is used in surface treatment products that increase the coefficient of friction on tile flooring, in addition to concentration, pH also plays a large part in determining the potency of glycolic acid in solution. Physician-strength peels can have a pH as low as 0.6, glycolic acid is used to improve the skins appearance and texture. It may reduce wrinkles, acne scarring, hyperpigmentation and improve many other conditions, including actinic keratosis, hyperkeratosis. Once applied, glycolic acid reacts with the layer of the epidermis. This allows the stratum corneum to be exfoliated, exposing live skin cells, highly purified grades of glycolic acid are commercially available for personal care applications. Glycolic acid is an intermediate for organic synthesis, in a range of reactions including, oxidation-reduction, esterification