4- Cresol

As a result of the high reactivity of phenol, alkylation takes place with olefins and alcohols under relatively mild conditions. Methylphenols, i.e. o-, m- and p-cresol, can be produced as a mixture by the alkylation of phenol with methanol. Since reactivity is increased by the introduction of the methyl group, alkylation of cresols to produce xylenols occurs under even milder reaction conditions. The long-chain alkylphenols are also produced by alkylation of phenol. 

The mono-methyl derivatives of phenol, the cresols, were discovered in coal tar in 1854 by Alexander Wilhelm Williamson. Coal tar then became the most important source of cresols for a century. Until the mid-1960 s, the natural sources for cresols were largely adequate. 

The proportion of cresols in the tar acids of coal tar is between 40 and 50% cresols are recovered jointly with phenol from the carbolic oil fraction of coal tar. A second source of cresols are refinery waste streams, arising during processing of heavy naphtha fractions from crackers, which contain about 60% cresol. 

A third natural source of alkylated phenols is coal gasification with tar byproducts (SASOL), complemented by the future possibility of cresols in the gasoline and middle-oil cuts from coal liquefaction. 

In the commercial synthesis of cresols, the most common processes are alkaline hydrolysis of chlorotoluene, the cleavage of cymene hydroperoxide and the alkylation of phenol in the gas phase with methanol. Alkali fusion of toluenesulfonic acids has largely lost its earlier significance, because of the inorganic salts which are co-produced. 

---

Usually prepared from the corresponding sulphonic acids by alkali fusion, methylation of phenol or from the aminotoluene by treatment with nitrous acid followed by boiling. Both o- and p-cresol are used as end components in azo dyes. 

For uses see cresylic acids. U.S. production of cresylic acid and mixed cresols 1978 65 000 tonnes. 

DNOC See 4,6-dinitro-o-cresol. dodecahedral co-ordination Co-ordination by... 

MCPA, l-methyl-A-chlorophenoxyacetic acid, Methoxone, CgH ClOj. Made by chlorination of o-cresol followed by reaction with chloroethanoic acid. While crystals, m.p. 118-119 C. As usually obtained, crude MCPA contains both 4- (60%) and 6- (40%) chloro-isomers, and is a light brown solid. Selective weedkiller. 

Phenol, 0-, m- and p-cresol, catechol, resorcinol, hydro-quinone (and other nuclear substituted phenols), 1 - and 2-naphthoi... 

Dissolve a few crystals of phenol in water and add ferric chloride solution a violet coloration is produced. Repeat, using i 2 drops of m-cresol shaken up with about i ml. of water a violet coloration is again produced. Catechol (in dilute solution) gives a green coloration. 

Physical properties. All solid except m -cresol, CH3CJH4OH, which is a liquid. All colourless when pure, but frequently slightly coloured due to atmospheric oxidation. All have in varying degrees a characteristic odour of carbolic acid. Phenol, the cresols and resorcinol have a caustic action on the skin. 

TEST Phenol Resorcinol 1 Hydro-Catechol 1 quinone e-Cresol m-C resol p-C resol i-Naphthol 2-Naphthol... 

If the third substance dissolves in both liquids (and the solubility in each of the liquids is of the same order), the mutual solubility of the liquids will be increased and an upper C.S.T. will be lowered, as is the case when succinic acid or sodium oleate is added to the phenol - water system. A 0 083 molar solution of sodium oleate lowers the C.S.T. by 56 -7° this large effect has been applied industrially in the preparation of the disinfectant sold under the name of Lysol. Mixtures of tar acids (phenol cresols) do not mix completely with water at the ordinary temperature, but the addition of a small amount of soap ( = sodium oleate) lowers the miscibility temperature so that Lysol exists as a clear liquid at the ordinary temperature. 

The solution must be strongly acid in order to avoid the coupbng reaction between the undecomposed diazonium salt and the phenol (see under Azo Dyes). For the preparation of phenol and the cresols, the aqueous solution of the diazonium compound is warmed to about 50° at higher temperatures the reaction may become unduly vigorous and lead to appreciable quantities of tarry compounds... 

Similarly CH3C,H4NH, (toluidines) — CH3C,H,OH (cresols). 

Dissolve the solid in 700 ml. of water in a 1500 ml. round-bottomed flask, and add a solution of 88 ml. of concentrated sulphuric acid in about 200 ml. of water until the liquid has a distinct odour of sulphur dioxide sufficient heat will be liberated in the neutralisation to cause the solution to boil. Immediately steam distil the liquid (Fig. II, 40, 1 it is better to use the apparatus shown in Fig. II, 41, 3) until a sample of the distillate gives only a slight precipitate with bromine water. About 700 ml. of distillate should be collected. Saturate the steam distillate with salt, extract the dl with ether, dry the extract with a little anhydrous magnesium or calcium sulphate, distil oflF the ether (compare Fig. II, 13, 4, but with a 50 ml. Claisen flask replacing the distilling flask) and distil the residue under diminished pressure. Collect the p-cresol at 95-96°/15 mm. the colourless liquid solidifies to a white crystalline solid, m.p. 31°. The yield is 24 g. 

No cresol is obtained if sodium hydroxide alone is used, presumably because the fused sodium hydroxide has no solvent action upon the sodium p-toluene-sulphonate. Potassium hydroxide alone gives excellent results, as do also mixtures of Sodium and potassium hydroxide containing not less than 28 per cent, of potassium hydroxide. The experimental details utilise the minimum amount of potassium hydroxide for the salce of economy. 

Moat phenols are crystalline solids notable exceptions are m-cresol and o-bromophenol. The monohydric phenols generally have characteristic odours. The solubihty in water increases with the number of hydroxl groups in the molecule. 

The melting points of some 0-aryl saccharin derivatives are phenol, 182° o-cresol, 163° m-cresol, 146° p-cresol, 172° o-nitrophenol, 236° p-nitrophenol, 192°. 

Thio-p-cresol (p-tolyl mercaptan), p-CHjCjH SH. This compound may be similarly prepared from p-toluenesulphonyl chloride (Section IV,207). The thio-p-cresol crystallises in the steam distillate and is collected and dried m.p. 43°. The b.p. under normal pressure is 194r-195°. 

Similarly o-sulphobeiizoic anhydride and o-cresol yields o-cresolsulphone-phthalein (o-cresol red) dibromination of the last-named gives dibromo-o-sulphonephthaleln (bromocresol purple) ... 

---