From alkenes

Carboxylic acids can also be prepared by oxidising alkenes with KMnO4 in dilute H2SO4: the alkene's C=C double bond is oxidatively CLEAVED apart, and each of the two alkene carbons ends up bearing its own -COOH group (or, for a more substituted alkene carbon, a ketone instead -- following the general pattern of oxidative alkene cleavage). Two worked examples: styrene (phenyl ethene, H5C6-CH=CH2), with KMnO4/dilute H2SO4/heat, is cleaved to give benzoic acid (H5C6-COOH) directly, since one alkene carbon carried the phenyl ring and the other carried only hydrogens (lost as CO2/formic-acid-type byproducts). Cyclohexene, being a CYCLIC alkene, behaves differently on cleavage: instead of splitting into two separate small fragments, cleaving its ONE ring double bond simply opens the …