Process for the preparation of indoles

A process for the preparation of 1-H- or 3-H-indoles of the formula ##STR12## by reaction of a phenylhydrazine of the formula ##STR13## which is unsubstituted in at least one ortho-position, with a ketone of the formula ##STR14## in an aqueous medium in the presence of an acid compound, where, in the formulae,

• R.sup.1 represents hydrogen or straight-chain or branched C.sub.1 -C.sub.4 -alkyl, which can be substituted by halogen, cyano or CON(R.sup.8,R.sup.9),
• R.sup.2 and R.sup.3 independently of one another denote hydrogen, straight-chain or branched C.sub.1 -C.sub.12 -alkyl, which can be substituted by halogen, cyano or CON(R.sup.8,R.sup.9), C.sub.5 -C.sub.6 -cycloalkyl or benzyl, at least one of the radicals R.sup.2 and R.sup.3 differing from hydrogen and it also being possible for R.sup.2 and R.sup.3 together to be C.sub.4 -C.sub.6 -alkylene or for R.sup.2 and R.sup.1 together to be C.sub.3 -C.sub.5 -alkylene,
• R.sup.4 and R.sup.5 independently of one another denote hydrogen or straight-chain or branched C.sub.1 -C.sub.4 -alkyl, which can be substituted by halogen,
• R.sup.6 and R.sup.7 independently of one another represent hydrogen, straight-chain or branched C.sub.1 -C.sub.12 -alkyl, straight-chain or branched C.sub.1 -C.sub.4 -alkoxy, phenyl, phenoxy, halogen, hydroxyl, nitro, cyano or N(R.sup.8,R.sup.9), it being possible for R.sup.6 additionally to denote CON(R.sup.8,R.sup.9), COR.sup.8 or COOR.sup.8, and
• R.sup.8 and R.sup.9 independently of one another represent hydrogen or straight-chain or branched C.sub.1 -C.sub.4 -alkyl,
• wherein less than 5 equivalents, based on 1 mol of phenylhydrazine, of an acid compound having a pK value of 1.3-4.5 are employed,