Salicylic acid and its Uses in manufacturing

Salicylic acid is an organic compound with the chemical formula HOC6H4COOH.It is a colorless, bitter-tasting solid that is a precursor and metabolite of aspirin (acetylsalicylic acid).It is a plant hormone,[9] and has been listed as an experimental teratogen on the EPA Toxic Substances Control Act (TSCA) list of chemicals.The name comes from the Latin salix, meaning willow.It is an ingredient in some acne-fighting products. Salicylic acid salts and esters are known as salicylates.

Medicine

Salicylic acid as a medicine is commonly used to remove the outer layer of the skin.Therefore, it is used to treat warts, psoriasis, acne vulgaris, ringworm, dandruff, and ichthyosis.Similar to other hydroxy acids, salicylic acid is an ingredient in many skin care products and is used to treat seborrheic dermatitis, acne, psoriasis, calluses, corns, keratosis pilaris, acanthosis nigricans, ichthyosis, and warts.

Uses in manufacturing 

Salicylic acid is used as a food preservative, fungicide and preservative.

Salicylic acid is used in the manufacture of other drugs, including 4-aminosalicylic acid, sandulpiride, and landetimide (via salethamide).Salicylic acid has long been a key ingredient in the manufacture of acetylsalicylic acid (aspirin).Aspirin (acetylsalicylic acid or ASA) is prepared by esterification of the phenolic hydroxyl group of salicylic acid with the acetyl group of acetic anhydride or acetyl chloride.ASA is the standard against which all other nonsteroidal anti-inflammatory drugs (NSAIDs) are compared.In veterinary medicine, this group of drugs is mainly used in the treatment of inflammatory musculoskeletal diseases.Bismuth subsalicylate, a salt of bismuth and salicylate, is the active ingredient in stomach remedies such as Pepto-Bismol, is the main ingredient in Kaopectate, and "shows anti-inflammatory effects (due to salicylic acid) and also acts as an anti-inflammatory Acids and mild antibiotics".Other derivatives include methyl salicylate, used as a liniment to soothe joint and muscle pain, and choline salicylate, used topically to relieve the pain of mouth ulcers.Aminosalicylic acid is used to induce remission in ulcerative colitis and has been used as an antituberculosis agent, often in combination with isoniazid.Sodium salicylate is a useful phosphor in the vacuum ultraviolet spectral range with an almost flat quantum efficiency in the wavelength range between 10 and 100 nm.It fluoresces blue at 420 nm. It is easily prepared on a clean surface by spraying a saturated methanolic solution of salt and then evaporating.

Mechanism of action

Salicylic acid modulates COX-1 enzyme activity to reduce the formation of pro-inflammatory prostaglandins. Salicylates may competitively inhibit the formation of prostaglandins.The antirheumatic (nonsteroidal anti-inflammatory) effects of salicylates are a result of their analgesic and anti-inflammatory mechanisms.When applied to the surface of the skin, salicylic acid works by making it easier for epidermal cells to shed, preventing clogged pores and allowing room for new cells to grow.Salicylic acid inhibits the oxidation of uridine-5-diphosphate glucose (UDPG) competitively with nicotinamide adenine dinucleotide and noncompetitively with UDPG.It also competitively inhibits the transfer of the glucuronyl group of uridine-5-phosphoglucuronic acid to the phenol receptor.The wound healing-delaying effect of salicylate may be mainly due to its inhibitory effect on mucopolysaccharide synthesis.

Safety

If a highly concentrated salicylic acid ointment is applied to most of the body surface, high levels of salicylic acid can enter the bloodstream, necessitating hemodialysis to avoid further complications.

Production and Chemical Reaction

Biosynthesis

Salicylic acid is biosynthesized from the amino acid phenylalanine.In Arabidopsis, it can be synthesized through a phenylalanine-independent pathway.

Industrial synthesis

Sodium salicylate is prepared by treating sodium phenoxide (the sodium salt of phenol) with carbon dioxide at high pressure (100 atm) and high temperature (115 °C), a process known as the Kolbe-Schmitt reaction.Acidification of the product with sulfuric acid gives salicylic acid:It can also be prepared by hydrolysis of aspirin (acetylsalicylic acid) or methyl salicylate (oil of wintergreen) with strong acids or bases.

Reaction:

Salicylic acid as its conjugate base is a chelating agent with an affinity for iron(III).Salicylic acid slowly degrades to phenol and carbon dioxide at 200–230 °C:

History

Willow has long been used for medicinal purposes.Dioscorides, whose writings spanned more than 1,500 years,used "Itea" (possibly a willow tree) to treat "painful bowel obstructions," birth control, "blood-spitters," removal of calluses, and corns, and used externally as a "gout warmer pack".William Turner repeated this in 1597, saying that willow bark "was burned to ashes and soaked in vinegar, which took away corns and other protuberances like feet and toes." Some of these remedies may describe the effect of salicylic acid, which can be extracted from the salicin present in willow. However, Hippocrates' use of willow as a pain reliever is a modern myth.Hippocrates, Galen, Pliny the Elder, and others knew that decoctions containing salicylates could relieve pain and reduce fever.It is used in Europe and China to treat these conditions.This remedy is mentioned in ancient Egyptian, Sumerian and Assyrian texts.The Cherokee and other Native Americans used the bark infusion to treat fevers and for other medical purposes, archaeologists discovered traces of salicylic acid on seventh-century pottery shards found in east-central Colorado.The Rev. Edward Stone, a clergyman from Chipping Norton, Oxfordshire, England, reported in 1763 that willow bark was effective in reducing fever.In 1828, German chemist Johann Andreas Buchner isolated and named a willow bark extract called salicin, after the Latin name for white willow (Salix alba).In 1829, the French pharmacist Henri Leroux isolated an even larger amount of the substance.Italian chemist Raffaele Piria was able to convert this substance into a sugar and a second component, which after oxidation became salicylic acid.In 1839, German researchers also isolated salicylic acid from the herb Filipendula ulmaria (formerly classified as Spiraea ulmaria).Their extracts can cause digestive problems such as stomach irritation, bleeding, diarrhea, and even death when consumed in large doses.In 1874, Scottish physician Thomas MacLagan experimented with salicin as a treatment for acute rheumatism, with considerable success, as he reported in The Lancet in 1876 like that.Meanwhile, German scientists tried sodium salicylate with little success and worse side effects.In 1979, salicylate was found to be involved in the induced defense of tobacco against tobacco mosaic virus.In 1987, salicylic acid was identified as a long-sought signal that causes heat production in thermogenic plants (eg Voodoo lily, Sauromatum guttatum).

Dietary source

Salicylic acid exists in plants in the form of free salicylic acid and its carboxylated esters and phenolic glycosides.Several studies have shown that humans metabolize measurable amounts of salicylic acid from these plants.Beverages and foods high in salicylates include beer, coffee, tea, various fruits and vegetables, sweet potatoes, nuts, and olive oil.Meat, poultry, fish, eggs, dairy products, sugar, bread, and grains are low in salicylates.Some people who are sensitive to dietary salicylates may experience symptoms of allergic reactions such as bronchial asthma, rhinitis, gastrointestinal disorders or diarrhea and may need to follow a low salicylate diet.

Plant hormone

Salicylic acid is a phenolic phytohormone that exists in plants and plays a role in plant growth and development, photosynthesis, transpiration, and ion uptake and transport.Salicylic acid is involved in endogenous signaling mediating plant defense against pathogens.It plays a role in resistance to pathogens (i.e., systemic acquired resistance) by inducing the production of pathogenesis-related proteins and other defensive metabolites.The defensive signaling role of SA is most clearly demonstrated by experiments in which it was abolished: tobacco or Arabidopsis were used to express nahG for salicylate hydroxylase, respectively.Pathogen inoculation did not produce the usual high SA levels, no SAR was produced, and there was no PR gene expression in leaves of the system. In fact, the subjects were more susceptible to virulent even often non-virulent pathogens.

On the exogenous side, salicylic acid can aid plant development by promoting seed germination,bud flowering, and fruit ripening, although high salicylic acid concentrations can negatively affect these developmental processes.The volatile methyl ester of salicylic acid, methyl salicylate, can also diffuse through the air, facilitating plant-to-plant communication.Methyl salicylate is taken up by the stomata of nearby plants, where it can induce an immune response after conversion back to salicylic acid.