The synthesis of 4,5-dihydroxytridecanoic, 5,6-dihydroxytetradecanoic, 9,10-dihydroxyoctadecanoic, 5,6-dihydroxy-12-methyltridecanoic, 5,6-dihydroxy-12-methyltetradecanoic, 5,6-dihydroxytetradecanedioic, 7,8-dihydroxyhexadecanedioic, and 9,10-dihydroxyoctadecanedioic acid by the desulphurisation of suitable substituted thiophens is described. The preparation of some derivatives of these acids is also described.