a process for the preparation of compounds of the formula : r . sub . n ar . sub . z comprises contacting compounds of the formula : r . sub . n ar . sub . z in the liquid phase , with hydrogen fluoride in the presence of molybdenum chloride wherein ar is aryl r is a substituent on the aryl nucleus selected from the group consisting of aryl , substituted aryl , halogen , alkyl , alkoxy , substituted alkyl , and substituted alkoxy ; n is 0 to 9 ; x is halogen atom other than fluorine ; w is 0 to 2 ; p is 1 to 3 ; w &# 39 ; is 1 to 3 , and is greater than w ; p &# 39 ; is 0 to 2 , and is less than p ; w + p is 3 ; w &# 39 ;+ p &# 39 ; is 3 ; z is 1 - 10 ; and the maximum value of n + z is 10 .