Sulphur esters

Sulphates or sulphuric esters of the long-chain fatty acids were the first alternative to the carboxylates. They are essentially the half esters of sulphuric acid (9.9) the ester incorporating the cetyl hydrophobe (9.10) belongs to the important class of fatty alcohol sulphates. Such sulphates, using C8-C18 hydrophobes, are common. 

Fig. 12.5 Determination of carbon-bonded sulphur, ester sulphate and total organic sulphurfrom analyses of total sulphur, hydriodic acid reduction, extractable inorganic sulphate, HCI digestion and Zn-HCI reduction.

Instead of the acid sulphuric ester of the alcohol, as in our example, the ester of another acid, e.g. benzoic, is often submitted to thermal decomposition, and so the charring action of the sulphuric add is avoided. 

Cellulose nitrated with nitric add vapour or by means of HN034-N205 mixtures demonstrates a significantly higher stability than nitrocellulose nitrated in a mixture of nitric and sulphuric add. This provides further evidence that the presence of sulphuric esters in nitrocellulose is responsible for its low stability. 

An interesting observation has been made while attempting to purify nitrocotton by dissolving it in acetone followed by predpitation with water. Guncotton (sample 1) was fairly well purified and stabilized by this method, but collodion cotton (sample 4) retained almost the whole amount of add present in it before purification and it was just as unstable as before, because the sulphuric esters were dissolved and reprecipitated with the nitrocellulose. Inddentally this is convincing chemical evidence confirming the existence of sulphuric acid cellulose esters in lower nitrated cellulose. 

Nitrocellulose dissolves in concentrated sulphuric acid, at the same time decomposing slowly, losing nitric add to form a sulphuric ester. 

Increase in the proportion of sulphuric acid in the mixture tends to reduce the chemical stability of the product, probably in consequence of the formation of unstable sulphuric esters of cellulose. 

The differences in values between the two kinds of nitrostarch are regarded by the authors as related to the presence of sulphuric esters in the nitrostarches prepared by means of mixed acids. 

The problem of how to stabilize nitrostarch has been solved by different means, but the majority of stabilization processes remain obscure as patent secrets. None the less, from certain observation some general conclusions can be made. It was early observed by Bechamp [13] that nitrostarch obtained by nitration in nitric acid alone is more stable than one obtained by means of nitric acid mixed with sulphuric acid. This has been confirmed experimentally by Hackel and T. Urbanski [18], and seems likely to be explained by the formation of starch sulphates or mixed nitric and sulphuric esters of starch. 

The other principal operation in the stabilization of nitrostarch is prolonged boiling, initially in acid water, and finally in alkaline water. As in the stabilization of nitrocellulose premature alkalization of the stabilizing medium is not recommended as this hinders the hydrolysis of sulphuric esters. Nevertheless in some American contributions (as mentioned above) early addition of ammonia for washing nitrostarch is reported to favour the formation of a stable product. 

To obtain these products selenium dioxide is allowed to react with the hydrogenated cinchona alkaloids or their derivatives in the presence of concentrated sulphuric acid and the products obtained are diluted with water and boiled. Selenohydroquinine is prepared from hydro-quinine sulphate or hydroquinine sulphuric ester, and forms yellow needles which remain unchanged below 235° C. selenoethylhydro-cupreine forms yellow needles, 5l.pt. 233° to 23-1° C., and selenohydro-cupreine separates as small, orange-coloured needles, w hich are unmelted below 235° C. The products are of use therapeutically. 

When cone, sulphuric acid acts on the alcohols, the acid esters only are formed, though sulphuric acid, by its great affinity for water, promotes almost complete esterification in other instances for the preparation of normal sulphuric esters, see Preparation 210. 

The reaction is usually carried out under pressure, and the yield is improved by the presence of sodium or ammonium sulphite (Bucherer s method), the sulphurous esters of phenols reacting more readily than... 

However, displacement of sulphur ester groups such as tosylate [183], mesylate [184] and triflate [185] groups are of much greater synthetic importance. These excellent leaving groups are readily displaced by an active source of fluoride ion this process represents an efficient method for the overall transformation of hydroxyl groups to fluorinated derivatives (Figure 3.33). 

That is, unlike the sulphuric esters, methyl sulphuric acid and dimethyl sulphate, it does not split off its alkyl group on hydrolysis, but oifly the chlorine atom. 

These iso compounds are obtained from the thio-cyanates by heat and their constitution is analogous to that of the alkyl iso-cyanates. They are not true sulphur esters but the alkyl radical is linked to nitrogen as is proven by their hydrolysis to primary amines. 

The mechanism of the reactions involved in the synthetic process for preparing this compound has been explained by Heymann (Berl. Ber. 1891, p. 3066). The yellow solution resulting from the action of the sulphuric anhydride on phenyl-glycine contains the sulphonic acid of indoxyl-sulphuric ester. On dilution of this solution, oxidation is effected by the sulphuric anhydride. 

Sulphates. These include sulphuric esters together with any inorganic sulphate (CaSO ). Dunnicliff gives the following method g, of nitrocellulose is heated on a water-bath with 50 c,c. cone, nitric acid until the nitrocellulose has dissolved and brown fumes have ceased. About 1 g. sodium chlorate is added in small quantities and the whole evaporated to dryness. The residue is treated with 20 c-c. of hydrochloric acid and 0 5 sodium chlorate (added in small quantities) and the liquid again evaporated to dryness. This latter treatment is repeated. This converts all sulphuric esters to soluble. sulphate, which may be estimated in the usual way. A blank test is made to allow for sulphate in the reagents. 

The original Bader and Sunder process was simplified considerably by the discovery of Morton Sundour Fabrics that the sulphuric ester can be formed as a metal complex by the action of fuming sulphuric acid, or an alkyl ester of chlorosulphonic acid, on the oxidized vat pigment in the presence of pyridine. The complex is finally converted into the sodium salt by the action of sodium hydroxide as shown in the series of reactions below ... 

Seal Swell Agents, as sulphurized esters, but which can affect frictional characteristics at high levels,... 

From the aspects of widespread occurrence, phosphate and sulphur esters are of the greatest importance. The study of hydrolysis of monophosphate esters shows that alcohol or phenolic forms split more readily... 

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