Thymol, preparation

Acetoxymercuri thymol, prepared in the usual manner, forms a lustrous, white powder, M pt. 147° C., decomposing at 182° C., and giving an immediate precipitate with ammonium sulphide, but with hydrogen sulphide only in the presence of hydrochloric acid. With so dium chloride the 2 chloromercuri derivative is formed, M.pt. 144° to 145° C., decomposing about 160° Tliis compound is probably... 

To prepare the standard pH buffer solutions recommended by the National Bureau of Standards (U.S.), the indicated weights of the pure materials in Table 8.15 should be dissolved in water of specific conductivity not greater than 5 micromhos. The tartrate, phthalate, and phosphates can be dried for 2 h at 100°C before use. Potassium tetroxalate and calcium hydroxide need not be dried. Fresh-looking crystals of borax should be used. Before use, excess solid potassium hydrogen tartrate and calcium hydroxide must be removed. Buffer solutions pH 6 or above should be stored in plastic containers and should be protected from carbon doxide with soda-lime traps. The solutions should be replaced within 2 to 3 weeks, or sooner if formation of mold is noticed. A crystal of thymol may be added as a preservative. 

Camphor [126-04-5] (11), menthol [89-78-1] (12), and thymol [89-83-8] (13) ate used in topical over-the-counter cough and cold preparations. Camphor is isolated from the camphor tree, Cinnomomum camphora T. Nees Eherneier, or prepared synthetically from a-pinene or isobomeol. About 75% of the camphor sold in the United States is synthetic. Menthol, commercially the most important terpene alcohol, is obtained by crysta11i2ation from... 

Thymoquinone has been prepared directly from thymol by sulfonating and oxidizing the sulfonation mixture with manganese dioxide or potassium dichromate the same process has been successfully applied to carvacrol. The oxidation of sa ts of aminothymol with dichromate, ferric chloride, or nascent bromine also leads to satisfactory yields of thymoquinone. The above procedure is based on the observation that the diazonium salt obtained from aminothymol is almost quantitatively con-... 

The most reliable work on the isomeric menthols is that of Pickard and Littlebury.2 Starting from the mixture of alcohols which Brunei had obtained by the reduction of thymol, and which he had described under the name of thymomenthol, they isolated from it about 60 per cent, of isomeric menthols, 30 per cent, of menthones, and several other compounds. They prepared the phthalic acid esters and converted them into their magnesium and zinc salts, which were then fractionally crystallised. 

According to Read and Smith i piperitone is, under natural conditions, optically inactive. By fractional distillation under reduced pressure, it is prepared, by means of its sodium bisulphite compound, in a laavo-rotatory form. The slight laevo-rotation is probably due to the presence of traces of cryptal. By fractional distillation alone, it is usually obtained in a laevo-rotatory form whether this is due to decomposition products or not is unknown. Piperitone has a considerable prospective economic value, as it forms thymol by treatment with formic chloride, inactive menthone by reduction when a nickel catalyst is employed, and inactive menthol by further reduction. Its char-Mters are as follows —... 

Smith and Penfold have shown that thymol can be prepared by the action of-ferric chloride on piperitone. 

Phillips and Gibbs S have summarised the history of the preparation of thymol synthetically and gives the following interesting account thereof. 

Mr. Max Phillips himself has taken out the following important patent for the preparation of thymol from para-cymene. 

The latest patent for the preparation of artificial thymol is that of E. M. Cole (U.S.P. 1,378,939, 24 May, 1921). His method consists essentially in the electrolytic reduction of nitro-cymene in the presence of sulphuric acid, and the subsequent diazotisation and reduction of the para-amidocymenol produced, by e ctric action, involving the use of stannous chloride. 

Procedure B. The experimental details for the preparation of the initial solution are similar to those given under Procedure A. Titrate 25 or 50 mL of the cold solution with standard 0.1M hydrochloric acid and methyl orange, methyl orange-indigo carmine, or bromophenol blue as indicator. Titrate another 25 or 50 mL of the cold solution, diluted with an equal volume of water, slowly with the standard acid using phenolphthalein or, better, the thymol-blue cresol red mixed indicator in the latter case, the colour at the end point is rose. Calculate the result as described in the Discussion above. 

Mixed indicator. This should be prepared from 1 part of 0.1 per cent neutralised aqueous cresol red and 3 parts of 0.1 per cent neutralised thymol blue. 

Maximum suppressors. Gelatin is widely used as a maximum suppressor in spite of the fact that its aqueous solution deteriorates fairly rapidly, and must therefore be prepared afresh every few days as needed. Usually a 0.2 per cent stock solution is prepared as follows. Allow 0.2 g of pure powdered gelatin (the grade sold for bacteriological work is very satisfactory) to stand in 100 mL of boiled-out distilled water for about 30 minutes with occasional swirling warm the flask containing the mixture to about 70 °C on a water bath for about 15 minutes or until all the solid has dissolved. The solution must not be boiled or heated with a free flame. Stopper the flask firmly. This solution does not usually keep for more than about 48 hours. Its stability may be increased to a few days by adding a few drops of sulphur-free toluene or a small crystal of thymol, but the addition is rarely worth while and is not recommended. 

Other SC- and BSC-PEG derivatives were prepared using the same general protocol. The active carbonate contents of the products were determined according to Kalir et al. (77) by reacting aliquots of the polymers with an excess of benzylamine and back titration of the latter with perchloric acid in dioxane using thymol blue as an indicator. The results of these determinations are summarized in Table I. 

The Japanese scientists tested the fiber optic carbon dioxide sensor86, prepared by dip-coating method - the sol-gel film containing indicator dye, thymol blue, was deposited on unclad fiber. The sensitive film had both organic and inorganic parts with good permeability. The differences between attenuation in N2 gas and in CO2/N2 mixture gas increased with the CO2... 

For preparing a eutectic mixture, a pharmacist needed 1/4 gr of thymol. If a pharmacist weighs that amount on a prescription balance with a sensitivity requirement of 1/10 gr, what would be the percent error ... 

The preparation of the sample prior to its analysis will depend upon the nature of both the sample and the analytical method chosen and may involve the disruption of cells, homogenization and extraction procedures as well as the removal of protein or other interfering substances. It may be necessary to prevent the decomposition and degradation of the carbohydrate content during such treatments or during storage by the addition of antibacterial agents such as thymol or merthiolate, or substances such as fluoride ions, which will inhibit the enzymic transformation of the carbohydrates. 

Monoterpenes, 10-carbon-containing terpenoids, are composed of two isoprene units, and found abundantly in plants, e.g. (+)-limonene from lemon oil, and (—)-linalool from rose oil. Many monoterpenes are the constituents of plant volatile oils or essential oils. These compounds are particularly important as flavouring agents in pharmaceutical, confectionery and perfume products. However, a number of monoterpenes show various types of bioactivity and are used in medicinal preparations. For example, camphor is used in liniments against rheumatic pain, menthol is used in ointments and liniments as a remedy against itching, bitter-orange peel is used as an aromatic bitter tonic and as a remedy for poor appetite and thymol and carvacrol are used in bactericidal preparations. 

Methylthymol blue and methylxylenol blue, prepared by the Mannich reaction from thymol-sulfonphthalein and p- xylenol blue respectively, have been intensively studied and resemble xylenol orange in many respects. If only one chelating group is introduced into cresol red, semi-xylenol orange results which is a common contaminant in XO and proves to be a more sensitive reagent for zirconium. 

The characteristic odour of ajowan oil is due to the high content of thymol (61%). Thymol easily crystallizes out from the oil and is sold in Indian markets as ajowan ka-phool, or sat-ajowan, and is much valued in medicines. Thymol is used as an ingredient of deodorants, mouthwashes, toothpastes and many pharmaceutical preparations. The leftover residue after distillation contains 15-17% protein and 20-25% fat and is valued as cattle feed. The major processed products are ajowan oil, oleoresin, thymol, thymol crystals, dethymolized oil (thymene) and fatty oils (Malhotra and Vijay, 2004). 

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