1 , 1 , 3 , 3 - substituted hydroxy indanes having the formula ## str1 ## wherein r 1 , r 2 and r 3 , which may be the same or different , are selected from the group of hydrogen , halogen and optionally substituted alkyl , cycloalkyl , aralkyl and aryl , in addition to which r 2 and r 3 , when they are in the ortho position relative to one another , may be taken together with the carbon atoms of the benzene ring to which they are attached to form a 5 membered carbocyclic ring , r 4 is ## str2 ## wherein r 10 and r 11 , which may be the same or different , are selected from the group of hydrogen and optionally substituted alkyl , cycloalkyl , aralkyl and aryl , and r 5 , r 6 , r 7 , r 8 and r 9 , which may be the same or different , are selected from the group of optionally substituted alkyl , cycloalkyl , aralkyl and aryl , the arrangement being such that r 5 and r 10 and / or r 6 and r 7 and / or r 8 and r 9 may form together with the carbon atoms to which they are attached a cycloaliphatic ring in addition to which r 6 and / or r 7 may also represent hydrogen .