Thymol solution

In the known absence of bromoform, iodoform, chloral, and other halogenated methanes, the formation of phenyhsonitrile with aniline provides a simple and faidy sensitive but nonspecific test for the presence of chloroform, the carbylamine test. Phenyhsonitrile formation is the identification test given in the British Pharmacopoeia. A small quantity of resorcinol and caustic soda solution (10% concentration) added to chloroform results in the appearance of a yellowish red color, fluorescing yeUow-green. When 0.5 mL of a 5% thymol solution is boiled with a drop of chloroform and a small quantity of potassium hydroxide solution, a yellow color with a reddish sheen develops the addition of sulfuric acid causes a change to brilliant violet, which, diluted with water, finally changes to blue (33). 

Immediately after the external and visceral examinations and before the Alizarin Red S staining, the fetuses may be kept in thymol solution, for up to 7 days for rat, mouse, and minipig fetuses and 10 days for rabbit fetuses. Thymol has proven antibacterial activity (4-6). 

Borax, Na2B4O7,10H2O, Mol. Wt. 38T4. Borax hydrolyses in aqueous solution to boric acid and sodium hydroxide and hence has an alkaline reaction. When borax is titrated with a strong acid to methyl orange or methyl red, the end-point is quite sharp and occurs when the acid is entirely in the free state, as boric acid is quite unaffected by these indicators. The B.P. method is by this titration. 1 ml 0 5N — 0 09536 g. It can then be titrated as described above under Boric Acid. The second titration should be double that of the first any disagreement would indicate excess of boric acid or alkali, and this fact is used for mixtures of borax and sodium bicarbonate such as Alkaline Nasal Solution-tablets, j5.P.C, and Compound Thymol Solution-tablets, B.P.C. Ashing to eliminate interference from dye is necessary in the latter product. 

Piperitone is of considerable technical im portance. It is a colourless oil of a pleasant peppermint-like smell. (-)-Piperilone has b.p. 109-5-110-5 C/I5mm. Piperitone yields thymol on oxidation with FeCl. On reduction with hydrogen in presence of a nickel catalyst it yields menthone. On reduction with sodium in alcoholic solution all forms of piperitone yield racemic menthols and womenthols together with some racemic a-phel)andrene. 

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. 

A. Nilrosothymol.—To a solution of 100 g. (0.666 mole) of thymol in 500 cc. of 95 per cent ethyl alcohol is added 500 cc. of concentrated hydrochloric acid. This mixture is cooled to 0° in a 2-1. beaker set in an ice-salt bath, and to it is added 72 g. (i mole) of commercial sodium nitrite in portions of about 5 g. each. 

Id the esthnatiou of carracrol a slight modiheatioo of this method EDDst he made, because carvacrol le thiot n down as a finely diyided white precipitate, giving the solution a milky appearance, lu order to form a precipitate the liquid is vigorously shaken after the addiliou of iodiue solution, and is sntiseqnently filtered. Then the liquid ia acidn-lated with hydrochloric acid, aud subsequently the same procedure is followed as was described lor thymol. The calculatiou is also the same. 

Thymol forms a soluble compound with alkalis, and can be extracted from the oils in which it occurs by shaking with a 5 per cent, solution of caustic soda or potash. 

After the electrolytic action. has continued for a suitable period, the contents of the vessel are allowed to cool, following which the unchanged nitro-cymene is separated for re-use, and the l-methyl-2-amino-4-iso-propyl-5-hydroxy benzol is filtered off from the remaining acid solution, whidh latter is strengthened for re-use. The l-methyl-2-amino-4-isopropyl-5-hydroxy benzol is then diazotised, and further reduced in an alkaline solution of stannous chloride, in the usual and well-known manner, with the resulting- production of thymol (l-methyl-4-isopropyl-5-hydroxy benzol). 

It is interesting to note that thymol, as well as its isomer carvacrol can be removed from its alkaline solution either by distillation by steam, or by repeated extraction by ether... 

On treatment with hydrobromic acid in acetic acid solution it yields thymol. 

The alkaline solution of thymol is made up to 100 or 200 c.c. as the case may require, using a 5 per cent, soda solution. To 10 c.c. of this solution in a graduated 500 c.c. flask is added a normal iodine solution in shgbt excess, whereupon the thymol is precipitated as a dark reddish-brown iodine compound. In order to ascertain whether a sufficient quantity of iodine has been added, a few drops are transferred into a test tube and a few drops of dilute hydrochloric acid are added. When enou iodine is present, the brown colour of the solution indicates the presence of io ne, otherwise the liquid appears milky by the separation of thymol. If an excess of iodine is present, the solution is slightly acidified with dilute hydrochloric acid and diluted to 500 c.c. From this 100 c.c. are filtered,off, and the excess of iodine determined by titration with normal solution of sodium thiosulphate. For calculation, the number of cubic centimetres required is deducted from the number of cubic centimetres of normal iodine solution added and the resultant figure multiplied by 5, which gives the number of cubia centimetres of iodine required by the thymol. 

Every cubic centimetre of normal iodine solution equals G 003753 gram of thymol. Knowing the quantity of thymol in the alkaline solution, the percentage in the original oil is readily found. 

In order that the reaction may proceed rapidly it is important to shake the mixture thoroughly after adding the iodine solution. When this is done the iodine compound is formed completely within one minute. With thymol it affords thymol di-iodide. In order to make sure that any iodine wnich may have entered into the hydroxyl-group is again liberated, care should be taken that a little hydriodic acid is always present hence the addition of the potassium iodide solution before the exc ess of iodine is titrated back with thiosulphate. Titration can only be regarded as complete when the blue coloration does not return in 10 minutes. 

The pFL-dependent partitioning of the ionizable, cationic dye thymol blue has also been investigated [6]. In its neutral, zwitterionic, and monoanionic forms, the dye preferentially partitions into the IL phase (from acidic solution), the partition coefficient to the IL increasing with increasing IL hydrophobicity. Under basic conditions, the dye is in the dianionic form and partitions into water (Figure 3.3-9). 

Sulphonphthaleins. These indicators are usually supplied in the acid form. They are rendered water-soluble by adding sufficient sodium hydroxide to neutralise the sulphonic acid group. One gram of the indicator is triturated in a clean glass mortar with the appropriate quantity of 0.1 M sodium hydroxide solution, and then diluted with water to 1 L. The following volumes of 0.1 M sodium hydroxide are required for 1 g of the indicators bromophenol blue, 15.0 mL bromocresol green, 14.4 mL bromocresol purple, 18.6 mL chlorophenol red, 23.6 mL bromothymol blue, 16.0 mL phenol red, 28.4 mL thymol blue, 21.5 mL cresol red, 26.2 mL metacresol purple, 26.2 mL. 

Thymol blue is used extensively as an indicator for titrations of substances acting as acids in dimethylformamide solution. It is used as a 0.2 per cent w/v solution in methanol with a sharp colour change from yellow to blue at the end point. 

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. 

A slight excess of 10 per cent barium chloride solution is added to the hot solution to precipitate the carbonate as barium carbonate, and the excess of sodium hydroxide solution immediately determined, without filtering off the precipitate, by titration with the same standard acid phenolphthalein or thymol blue is used as indicator. If the volume of excess of sodium hydroxide solution added corresponds to timL of 1M sodium hydroxide and u mL 1M acid corresponds to the excess of the latter, then v — v = hydrogencarbonate, and V— v — v ) = carbonate. 

In the second procedure a portion of the cold solution is slowly titrated with standard 0.1M hydrochloric acid, using phenolphthalein, or better, the thymol blue-cresol red mixed indicator. This (say, YmL) corresponds to half the carbonate (compare Section 10.32) ... 

Mixed indicator solution. Mix two volumes of 0.1 per cent phenolphthalein solution and three volumes of 0.1 per cent thymol blue solution (both in ethanol). 

Pipette 25 mL barium ion solution (ca 0.01 M) into a 250 mL conical flask and dilute to about 100 mL with de-ionised water. Adjust the pH of the solution to 12 by the addition of 3-6 mL of 1M sodium hydroxide solution the pH must be checked with a pH meter as it must lie between 11.5 and 12.7. Add 50 mg of methyl thymol blue/potassium nitrate mixture [see Section 10.50(C)] and titrate with standard (0.01 M) EDTA solution until the colour changes from blue to grey. 

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