Guaiacol

In a 5-I. flask fitted with a stirrer, a thermometer reaching to the bottom, a fractionating column about 40 cm. long (Note 2), and a return inlet tube, are placed 912 g. of crystalline guaiacol and 1500 g. of 48 per cent hydrobromic acid. This apparatus is connected with a condenser, an automatic separator, and an absorption vessel, as shown in the diagram (Note 1). The 

After six to seven hours, the temperature at the head of the column begins to rise above 95° and finally reaches 98°, at which point practically no more guaiacol passes over with the distillate. This requires about one hour more, after which the heating is stopped (Note 5). The increase in weight of the absorption 

The residue in the flask, which has become pink in color, is extracted at 85-95° with three 1500-cc. portions of toluene, and the united extracts are distilled under reduced pressure on the steam bath until no more moisture passes over with the vapor. The solution (2-2.5 h) is then allowed to cool, whereupon 385-390 g. of catechol separates in colorless plates melting at 104-105°. The mother liquor is further concentrated under reduced pressure and the residue finally distilled, pure catechol passing over at 124-125 °/12 mm. The distillate, on recrystallization from a small quantity of toluene, yields 8-10 g. of pure material. 

The aqueous residue from the three extractions with toluene yields, when the bulk of the water has been distilled off on the steam bath under reduced pressure, a further quantity of catechol by extraction with hot toluene, but the crystals so obtained are contaminated with a red impurity. It is therefore preferable to distil the entire residue, again collecting the fraction boiling at 124—1250/12 mm. and recrystallizing it from fresh toluene. In this way 295-305 g. of pure product is obtained. The forerun contains a little aqueous hydrobromic acid, which may be employed in a subsequent batch. The total yield of pure catechol is 690-705 g. (77-80 per cent of the theoretical amount). 

Any column of standard form is suitable to work satisfactorily, it is unnecessary for it to be more than 40 cm. in length. 

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Medicinal creosote is a mixture of phenols, chiefly guaiacol and creosol (4-melhyl-2-meth-oxyphenol), obtained by distillation of wood tar. B.p. 480-500 K. It is almost colourless with a characteristic odour and is a strong antiseptic, less toxic than phenol. 

Guaiacol has a very characteristic odour and burning taste its medicinal properties are identical with those of creosote. Used in the preparation of vanillin and paparvarin and for denaturing alcohol. 

Into the reaction flask is added 912g crystalline guaiacol and 1500g regular 48% HBr which is then slowly heated to reflux. The tepid water condenser is there to allow the bro-momethane that is formed to leave the reaction flask but is still cold enough to keep the other reactants in the reaction flask. The noxious bro-moethane condenses in the cold water condenser and drips into the chilled methanol in the collection flask. This will keep this bromoethane trapped so that the chemist will not die... 

Technically, the chemist could avoid the complex glassware apparatus of this procedure for a more crude approach [104]. This report shows some dudes de-methylating an amphetamine with concentrated HCI in a pressure cooker. A similar approach with good yields was also employed in ref. 83 and should work as well or better on guaiacol. Hydroiodic acid or hydrobromic acid will work better than hydrochloric acid but, you know, whatever floats the chemist s boat. To do this the chemist can just plain reflux HI or HBr with the guaiacol for a few hours and process as before or she can use HI, HBr or HCI and place the reactants in a pipe bomb for a few hours. 

METHOD 3 [109]—1 part guaiacol and 2.5 parts MesSiSNa in 1,3-dimethyl-2-imidazoline heated at 185°C in a sealed pipe bomb gives 80-96% catechol. 

METHOD 4 [110, 111] - guaiacol and cupric perchlorate (Cu(CI04)2)-ascorbic acid (that s vitamin C, bubba ) are mixed in an appropriate solvent under oxygen atmosphere in a flask to give about 30% catechol. 

This is a nifty little way to turn catechol or guaiacol into protocate-chualdehyde or vanillin using what is called the Riemer-Tiemann reaction [137 p824, 138], It is a really ancient reaction and only works on benzene molecules that have an OH group. One needs to use KOH instead of NaOH because it is better at promoting para substitutions (don t ask). And if one is going to make vanillin from guaiacol then there needs to be a little ethanol in the reaction as well. 

When making vanillin from guaiacol the chemist can smell success because the product will have an intense vanilla odor. One can even flavor cookies with the stuff (true ). This Riemer-Tiemann method is also an excellent way to get salicylal-dehyde from phenol in yields of up to 50%. The chemist does everything the same except uses NaOH instead of KOH. 

When camphene reacts with guaiacol (2-methoxyphenol), a mixture of terpenyl phenols is formed. Hydrogenation of the mixture results ia hydrogenolysis of the methoxy group and gives a complex mixture of terpenyl cyclohexanols (eg, 3-(2-isocamphyl) cyclohexanol [70955-71 (45)), which... 

In 1874, Tiemann and Ha arm ann examined the stmcture of vanillin and reported it to be 3-methoxy-4-hydroxybenzaldehyde. This was not a difficult task because, on treatment with potassium hydroxide, vanillin (1) gave protocatechaic acid [99-50-3] (2), which, in turn, was decarboxylated to catechol [120-80-9] (3) by dry distillation (eq. 1). As both compounds were known at that time, the position of the substituent groups in vanillin was estabHshed. Finally, Reimer synthesized vanillin from guaiacol [90-05-1] and thus proved the identity of its stmcture. In 1894 RhcJ)ne-Poulenc began producing vanillin on an industrial scale. Since then, many other producers have entered into vanillin production, often only to leave it behind. 

The manufacture of vanillin shows the progress made in the chemistry and chemical engineering of the substance. Most commercial vanillin is synthesized from guaiacol the remainder is obtained by processing waste sulfite Hquors. Preparation by oxidation of isoeugenol is of historical interest only. 

This process has the advantage that, under the reaction conditions, the glyoxyl radical enters the aromatic guaiacol ring almost exclusively para to the phenoHc hydroxyl group. Tedious separation procedures are thus avoided. 

In contrast to vanillin from lignin, the principal impurity found in vanillin from guaiacol is 5-methyl vanillin, typically present at levels of about 100 ppm in Rhovanil Extra Pure (Rhc ne-Poulenc), although levels as high as 3000 ppm have been found in samples from other producers. This impurity is completely odorless. 

No residual guaiacol can be found in vanillin produced by the guaiacol process. In contrast to vanillin from lignin, vanillin from guaiacol is extremely consistent in quaUty owing to the consistency of the supply source, and shows no variation in taste, odor, or color. 

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