Phenols, from sulphonic acids reactions

From Sulphonic Acids.—As previously stated, the methods of formation of phenols are wholly different from those of alcohols, and, together with their reactions, prove the constitution to be as we have given it, viz.. Ring—OU. The synthesis which is most generally used industrially is that from sulphonic acids, i. 520). When a salt of benzene sulphonic acid is fused with potassium or sodium hydroxide, phenol is formed together with a sulphite salt of the metal, according to the following reaction ... 

Artificial humic acids were produced, either chemically or enzymatically, from a variety of phenols, from sulphonated napthoquinone, and fromp-benzoquinone, together with numerous amino acids. Microbial decomposition of both natural and artificial humic acids was usually negligible. When model humic acids were prepared by reacting quinones formed from phenols, usually with amino acids present, it was observed that oxidation, polymerization, and polycondensation were more rapid in the presence of amino acids than in their absence. Evidently the amino acids participate in these reactions. Colorless products were formed initially which gradually darkened to reddish-brown and then brownish-black. These humic acids had many physical and chemical properties that corresponded closely to those of natural humic acids. 

The most important reaction of the sulphonic acids is their conversion into phenols by fusion with caustic alkalis. When they are fused with potassium cyanide, nitriles are obtained, e.g. benzonitriie from ben-zenesulphonic acid. 

At one time the requirement for phenol (melting point 41°C), eould be met by distillation of eoal tar and subsequent treatment of the middle oil with eaustic soda to extraet the phenols. Such tar acid distillation products, sometimes containing up to 20% o-cresol, are still used in resin manufacture but the bulk of phenol available today is obtained synthetically from benzene or other chemicals by such processes as the sulphonation process, the Raschig process and the cumene process. Synthetic phenol is a purer product and thus has the advantage of giving rise to less variability in the condensation reactions. 

The kinetics of desulphonation of sulphonic acid derivatives of m-cresol, mesitylene, phenol, p-cresol, and p-nitrodiphenylamine by hydrochloric or sulphuric acids in 90 % acetic acid were investigated by Baddeley et a/.701, who reported (without giving any details) that rates were independent of the concentration of sulphuric acid and nature of the catalysing anion, and only proportional to the hydrogen ion concentration. The former observation can only be accounted for if the increased concentration of sulphonic acid anion is compensated by removal of protons from the medium to form the undissociated acid this result implies, therefore, that reaction takes place on the anion and the mechanism was envisaged as rapid protonation of the anion (at ring carbon) followed by a rate-determining reaction with a base. 

The crude product contains isomers other than that required and also nitrated phenolic compounds resulting from side reactions. The usual method of purification is to treat the crude product with sodium sulphite, which converts asymmetric trinitro compounds to sulphonic acid derivatives, and to wash out the resulting soluble products with alkaline water. The purity of the product is determined by the melting point, the minimum value for Grade I TNT commonly being 80-2°C. Unless adequate purity is achieved, slow exudation of impurities can occur during storage and the TNT then becomes insensitive. 

Alcohols may be prepared (1) by hydration of alkenes (1) in presence of an acid and (11) by hydroboratlon-oxidatlon reaction (2) from carbonyl compounds by (1) catalytic reduction and (11) the action of Grignard reagents. Phenols may be prepared by (1) substitution of (1) halogen atom In haloarenes and (11) sulphonic acid group In aiyl sulphonic acids, by -OH group (2) by hydrolysis of diazonium salts and (3) industrially from cumene. 

Polymeric phosphonium salt-bound carboxylate, benzenesulphinate and phenoxide anions have been used in nucleophilic substitution reactions for the synthesis of carboxylic acid esters, sulphones and C/O alkylation of phenols from alkyl halides. The polymeric reagent seems to increase the nucleophilicity of the anions376 and the yields are higher than those for corresponding polymer phase-transfer catalysis (reaction 273). 

Reaction LXXV. Fusion of Aromatic Sulphonic Acids with Caustic Alkalis. (Z. Ch (1876), 3, 299 J. pr., [2], 17, 394 20, 300.)—This method is of technical importance as it is employed to prepare phenols and naphthols from the parent hydrocarbons. These phenols and naphthols are much used as intermediates in the dye industry. The method cannot easily be applied to determine structure, owing to rearrangement liable to occur at the elevated temperatures. Caustic potash is more convenient than soda, since it generally yields a more easily fusible mixture. 

It dissolves somewhat more easily in phenol, with a bluish-green colour. With concentrated sulphuric acid it forms a violet solution, from which water precipitates the dark green sulphate. With fuming sulphuric acid it yields sulphonic acids differing according to the temperature and duration of the reaction. The sulphonic acids are green in the free state, and form easily soluble salts- with the alkalies. These latter have a violet-black colour. 

Through researches in aromatic chemistry it was not tong before synthetic phenol became available. Prior to work by Griess on aromatic diazo compounds published in 1860, Hunt (ref.1) had in 1849 obtained phenol from a diazonium salt produced by the reaction of aniline hydrochloride and siver nitrite. F.A. Kekule, (1829-1896), Fig.3, in 1867 (ref.2) described the recently completed sulphonation of benzene and fusion of the sulphonic acid with alkali as a new... 

Other processes include the alkylation of phenol using alkenes, and the manufacture of acrylate and methacrylate esters from alcohols and the corresponding acids. Olefin hydration reactions require more extreme conditions but Deutsche Texaco have developed a resin-catalysed propene hydration process to form isopropyl alcohol [125]. The reaction is run at 130 C near the upper limit for sulphonic acid resins, but a species with sufficient lifetime is available. There is even some evidence that butene hydration is now carried out similarly. Finally, B.P. Chemicals have recently disclosed [126] a new olefin isomerisation process yielding 2,3-dimethylbut-l-ene. Here the conditions required to favour the isomerisation versus rapid oligomerisation had to be identified to establish a viable process. 

Monomer grade bis-phenol S was not readily available and presented some difficulty as the product from reaction of phenol with sulphuric acid (as operated at that time) gave a product heavily contaminated with isomeric sulphones which was difficult to purify. However, work at Welwyn showed that 4-chlorophenyl 4-hydroxyphenyl sulphone was easily obtained in... 

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

Various dehydrating agents—concentrated sulphuric acid, zinc chloride, phosphorus pentoxide—can be used. Sulphuric acid, although perhaps the most convenient, has the disadvantage that it tends to sulphonate the aromatic substances employed. At a low temperature, however, diphenylmethane can be obtained from benzyl alcohol and benzene. At 140° phosphorus pentoxide condenses benzene and diphenylcarbinol to triphenylmethane (see B., 7,1204). Not only substituted benzyl alcohols, but even mandelic acid can be brought within the scope of the reaction, while in place of benzefte its nitro, amino or phenolic derivatives may be used. 

With benzenesulphonic add this important reaction does not take place smoothly for this reason the directions for carrying it out practically will be given later in another place (see /3-naphthol). Polyadd phenols may also be obtained from poly-basic sulphonic adds. The formation of m-dioxvbenzene or resordnol from benzenedisul-phonic acid is of practical value ... 

In contrast to aliphatic alcohols, which are mostly less acidic than phenol, phenol forms salts with aqueous alkali hydroxide solutions. At room temperature, phenol can be liberated from the salts even with carbon dioxide. At temperatures near the boiling point of phenol, it can displace carboxylic acids, e.g. acetic acid, from their salts, and then phenolates are formed. The contribution of ortho- and -quinonoid resonance structures allows electrophilic substitution reactions such as chlorination, sulphonation, nitration, nitrosation and mercuration. The introduction of two or three nitro groups into the benzene ring can only be achieved indirectly because of the sensitivity of phenol towards oxidation. Nitrosation in the para position can be carried out even at ice bath temperature. Phenol readily reacts with carbonyl compounds in the presence of acid or basic catalysts. Formaldehyde reacts with phenol to yield hydroxybenzyl alcohols, and synthetic resins on further reaction. Reaction of acetone with phenol yields bisphenol A [2,2-bis(4-hydroxyphenyl)propane]. 

Sulphonate salts may be formed by oxidation of aromatic thiocarbamates with hydrogen peroxide, in 50-60% yield243, as shown in equation 38. The thiocarbamates may be readily formed from phenols by reaction with dimethylthiocarbamyl chlorides244. A similar reaction also occurs on oxidation of thioacetates with hydrogen peroxide or peracids245,246. Thioacetates are readily prepared by several routes, for example, by reaction of alkenes with thioacetic acid. 

---