between 0 5 and 1 5 bar finally the carboxy group can be converted to the cox group stage c by known organic chemistry methods a i vogel u201c chimica organica pratica u201d casa editrice ambrosiana 3rd edition 1967 m b smith and j march u201c march 39 s advanced organic chemistry u201d wiley 6th edition 2007 preferably by treatment with thionyl chloride sulphuryl chloride phosphorus trichloride phosphorus pentachloride phosphorus oxychloride oxalyl chloride phosgene and even more preferably with thionyl chloride the reaction can be conducted in the presence of a solvent but in some cases the solvent function can be performed by an adequate excess of the halogenating agent the preferred solvents are all solvents compatible with the reagents and with the product of reaction and in particular with the halogenating agent and the cox group which is synthesised aromatic hydrocarbons such as benzene toluene and xylene saturated hydrocarbons such as pentane hexane cyclohexane heptane octane isooctane decane and isoparaffin halogenated solvents such as methylene chloride chloroform dichloroethane and trichloroethane ethers such as diethylether tetrahydrofuran and dioxane esters such as methyl acetate and ethyl acetate nitriles such as acetonitrile and ketones can be used in particular the preferred solvent is an aromatic hydrocarbon in particular toluene or xylene more preferably xylene the same solvent as used for stage b is preferably used the reaction can be conducted at temperatures between 10 u00b0 c and 150 u00b0 c preferably between 30 u00b0 c and 100 u00b0 c and even more preferably between 50 u00b0.