Monohydroxylation of unsaturated oils: I. Sulfation-hydrolysis and sultone-formation

Hydroxy unsaturated glycerides were sought from safflower and linseed oils by partial sulfation with sulfuric acid, followed by hydrolysis of sulfate to hydroxy groups. Sulfation of oleicrich oils or their fatty acids and subsequent hydrolysis (effected conveniently with acidified barium chloride) yielded hydroxy products corresponding to 50–70% of the monoene content. Sulfation of a mixture of methyl oleate and linoleate with 78% w/w of sulfuric acid was directed mainly at the oleate component. Safflower oil was partially sulfated without side reactions using 78% or 79% w/w of sulfuric acid, the hydrolyzed products showing hydroxyl value (HV) of about 35 for a loss of 13 units of iodine value (IV). Use of more concentrated sulfuric acid, and subsequent hydrolysis, led to sulfur-containing products which include sultones. Treatment of atrans,trans, but not of acis,trans conjugated diene with sulfuric acid led to sultone formation. It is postulated that when linoleate is sulfated with strong acids, acidisomerization to atrans,trans conjugated diene occurs, probably followed by 1,4-addition of -OH and -SO₃H and quick dehydration of these moieties to give a 1,4-sultone. Linseed oil was apparently sulfated without side reactions using 80% w/w sulfuric acid at 0–5 C and then hydrolyzed to a product of HV 77 and IV 159.