as used herein , the alkyl groups are preferably c 1 - c 20 alkyl groups and more preferably short - chain alkyl groups ( e . g . c 1 - c 4 ). furthermore , saturated , straight or branched alkyl groups are preferred ; however , they may optionally contain one or more unsaturations , e . g . one or more double bonds and / or be substituted , e . g ., with alkoxy or phenoxy groups . the aromatic substituents optionally present in the r 1 group or as r 3 , r 4 or r b groups are preferably carbocyclic ( monocyclic or polycyclic ) c 6 - c 20 aromatic groups , e . g . phenyl . when r a is acyl , it may in particular be r b co -, where r b is an alkyl or aromatic group , typically c 1 - c 4 alkyl . the r &# 39 ;, r &# 34 ;, r 3 and r 4 groups are preferably short - chain alkyl groups , typically c 1 - c 4 alkyl groups , i . e . containing 1 to 4 carbon atoms , more preferably -- ch 3 groups . in the derivatives of formula ( ii ), r 5 is preferably h and , when r 5 is c 1 - c 4 alkyl , is preferably -- ch 3 . r 2 is typically a protective group removable in an acid medium and stable to the bases , preferably an alkyl group , typically saturated and having a straight or branched short chain ( e . g . c 1 - c 4 ), preferably -- ch 3 . the r 1 , r 2 , r 3 and r 4 groups , present in the various chemical intermediates mentioned herein , may be varied , from one step to the other of the claimed processes , by known methods , depending on the requirements and according to the meanings reported herein or to equivalent meanings . for the purposes of the present invention , preferred groups of compounds are of formulas ( ii ) and ( iii ) above , in which r 1 is -- oh , r 2 is a saturated straight or branched alkyl group containing 1 to 4 carbon atoms ( c 1 - c 4 ), and for compounds of formula ( ii ), r 5 is h ; especially preferred are compounds of formulas ( ii ) and ( iii ) above in which r 1 is -- oh , r 2 is -- ch 3 , and for compounds of formula ( ii ), r 5 is h . the compounds of formula ( iii ) in which r 1 is -- oh , may be converted to the corresponding compounds of formula ( iii ), in which r 1 is or &# 39 ;, by treatment with an alcohol r &# 39 ; oh , in the presence of an acid catalyst , according to conventional methods . out of the compounds of formula ( iv ), the compounds in which r 2 is a saturated , straight or branched c 1 - c 4 alkyl group , and in particular ch 3 , are preferred . when r 1 is -- or &# 39 ;, -- nr &# 39 ; r &# 34 ; or sr &# 39 ;, r 1 conversion to -- oh typically takes place in an aqueous acid medium , in steps b &# 39 ;) or b &# 34 ;), and especially in step b &# 34 ;). yielding the corresponding phenol derivative of formula ( iv ) wherein the carboxyl function is free ; alternatively , it may be carried out by a further hydrolysis step , i . e . acid or basic . preferably , the reaction mixture coming from diazotisation ( step b &# 39 ;) is directly subjected to step b &# 34 ;) without prior isolation of the intermediate diazo derivative . step c ), i . e . removal of protective group r 2 , is preferably a step of acid hydrolysis , in an aqueous medium , of the compound of formula ( ii ) or ( iii ) or ( iv ), more preferably of formula ( iv ), in which r 2 is a protective group removable in an acid medium , typically c 1 - c 4 alkyl . step c ) is preferably carried out as the last step of the synthesis after performing , in sequence , steps a ), b &# 39 ;) and b &# 34 ;), on the compound of formula ( iv ) coming from step b &# 34 ;), in which r 1 is as defined above and r 2 is a protective group as defined above . according to a preferred embodiment of the present invention , step a ) utilizes the diphenylketone of formula ( ii ), in which r 5 is h , r 1 is -- oh , and r 2 is a c 1 - c 4 alkyl group , preferably saturated , straight or branched , more preferably ch 3 , to give the corresponding 1 - aminoanthraquinone derivative of formula ( iii ), in which r 1 is -- oh and r 2 is a saturated , straight or branched c 1 - c 4 alkyl group , preferably ch 3 ; the reaction mixture from step b &# 39 ;) is directly subjected to step b &# 34 ;), without prior isolation of the intermediate diazo derivative , to give the corresponding phenol derivative of formula ( iv ), in which r 2 is a saturated , straight or branched c 1 - c 4 alkyl ; in step c ), the derivative of formula ( iv ) as obtained above is subjected to acid hydrolysis to give the rhein of formula ( v ). according to a still more preferred embodiment of the present invention , the derivative of formula ( i ) is diacerhein , in which r a is -- ococh 3 . therefore , the process according to the present invention comprises acetylation ( step d ). the strong acids suitable for the conversion of diphenylketone of formula ( ii ) to the 1 - aminoantraquinone derivative of formula ( iii ) according to the present invention are for instance either mineral ( inorganic ) or organic acids , such as sulphuric acid and cf 3 so 3 h . for the present purposes , concentrated acids typically have a concentration of about at least 90 %, e . g . of about 95 %- 98 % weight by weight ( w / w ) of acid , e . g . in water . in present step a ) , superacids such as fuming sulphuric acid ( h 2 so 4 . so 3 , also known as oleum , with variable amount of so 3 or cf 3 so 3 can be used , or concentrated sulphuric acid ( e . g . about 95 %- 98 % w / w ). according to particular embodiments of the present invention , concentrated sulphuric acid or cf 3 so 3 h can be used , more preferably cf 3 so 3 h . step a ) is preferably carried out at a temperature approximately ranging from 0 ° c . to 250 ° c ., preferably from 100 ° c . to 200 ° c ., and more preferably from about 140 ° c . to 160 ° c . for example , the diphenylketone of formula ( ii ) and the selected strong concentrated acid are mixed under stirring at a temperature ranging from 0 ° c . to room temperature ( about 20 ° c . to 30 ° c . ); then the temperature is gradually raised preferably to a value ranging from about 100 ° to about 200 ° c ., typically at least about 140 ° c . to 160 ° c . the diphenylketone of formula ( ii )/ acid ratio typically ranges from 0 . 5 : 1 to 4 . 75 : 1 , e . g . about 1 : 3 , expressed as mmols of product ( ii ) per ml of strong acid . the product of formula ( iii ) is isolated by conventional methods : in particular it precipitates from the reaction medium , generally in the form of crystals , after neutralization with a strong base , e . g . naoh , preferably added at a low temperature . e . g . 4 ° c . to 8 ° c ., and is separated from the liquid phase by conventional methods , e . g . filtration . diazotisation ( step b &# 39 ;) is preferably carried out by cold treating the product of formula ( ii ) with nitrous acid , in an aqueous medium ; the reaction temperature preferably ranges from 0 ° c . to 8 ° c ., more preferably from about 0 ° c . to 5 ° c . nitrous acid is preferably generated in the reaction medium by the action of a strong acid ( e . g . an inorganic acid , such as h 2 so 4 , or an organic acid , such as cf 3 so 3 h , preferably h 2 so 4 ) on a nitrite , typically an alkali metal nitrite , such as nano 2 . for example , step b &# 39 ;) is carried out with nano 2 , in a concentrated h 2 so 4 / water mixture in a ratio ranging from 1 : 1 to 1 : 3 ( volume / volume = v / v ). the diazotising agent is typically used in molar excess of the compound of formula ( iii ), in a quantity ranging , e . g ., from about 1 . 1 to 2 . 0 mol , preferably of about 1 . 5 mol per mol of ( iii ). the diazotised intermediate of formula ( vi ) ## str13 ## in which r 1 and r 2 are defined as for the dimethylketone of formula ( ii ), can be isolated from the medium of diazotisation ( step b &# 39 ;), e . g . by filtration . x is the anion of the strong acid , in whose presence diazotisation is carried out ; n is the number ( integer ) corresponding to the number of negative charges of said anion ; when r 1 is h , m is ( n - 1 ), or , when r 1 is different from h , m = n . the diazo derivative of formula ( vi ) is preferably the one in which r 1 is -- oh , and r 2 is c 1 - c 4 alkyl , in particular ch 3 ; furthermore , x is preferably so 4 2 - ( n = 2 ), and m is 1 . in step b &# 34 ;) the strong acid is , e . g ., an inorganic acid , such as sulphuric acid , or an organic acid , such as cf 3 so 3 h ; sulphuric acid is typically used . step b &# 34 ;) is generally carried out at a temperature ranging from 100 ° c . to 250 ° c ., preferably of about 140 ° c . to 150 ° c . under typical conditions , the reaction medium of steps b &# 39 ;) and b &# 34 ;) is a strong acid / water mixture in a ratio preferably ranging from 1 : 0 . 5 to 1 : 5 , more preferably from 1 : 1 to 1 : 3 ( v / v ). furthermore , step b &# 39 ;) is preferably carried out with ratios of the derivative of formula ( iii ) to the reaction medium ranging from 1 : 0 . 5 to 1 : 5 , typically 1 : 3 , expressed as mmols of ( iii ) per ml of reaction medium ; step b &# 34 ;) is preferably carried out with ratios of substrate [ derivative of formula ( iii ) or derivative of formula ( vi )] to the reaction medium typically equal to about 1 : 3 , expressed as mmols of the derivative of formula ( iii ) or ( vi ) per ml of reaction medium ( typically a strong acid / water mixture ). the resulting phenol derivative of formula ( iv ) is easily isolated from the acid reaction mixture by cooling to room temperature and collecting the precipitate , e . g . by filtration . as mentioned above , step b &# 34 ;) is preferably carried out on the reaction mixture from step b &# 39 ;), optionally diluted , without prior isolation of the diazotisation product . for example , diazotisation is carried out in an acid aqueous medium , e . g . by optionally diluting with additional strong acid / water mixture the reaction mixture from step b &# 39 ;), then heating to the temperature of step b &# 34 ;). acid hydrolysis as per step c ) is preferably carried out at a temperature ranging from about 90 ° c . to about 160 ° c ., more preferably from about 100 ° c . to about 120 ° c . preferably , step c ) is carried out with concentrated hbr ( about 48 % hbr aqueous solution ) and glacial acetic acid as diluent ; the temperature is preferably the reflux temperature of the reaction mixture . the quantity of concentrated hbr ranges , e . g ., from about 0 . 1 ml to 10 ml , typically from 0 . 5 ml to 3 ml of concentrated hbr per mmol of substrate of formula ( ii ), ( iii ) or ( iv ). the quantity of glacial acetic acid ranges about from 5 to 20 ml , e . g . about 10 ml per mmol of substrate to be treated . under the conditions reported above , the reaction product from step c ), in particular the rhein of formula ( v ), generally precipitates in the reaction medium at room temperature , wherefrom is separated by conventional methods , e . g . by filtration in vacuo ; then it is preferably purified by crystallization , e . g . from an alcohol , such as methanol . the synthesis reactions as per steps a ), b &# 39 ;), b &# 34 ;) and c ) described above are completed within short times , generally ranging from about 15 min . to 2 - 14 3 hrs ., and give highly pure products in high yields . preferably , the derivative of formula ( i ) is the one in which r a is -- coch 3 ( diacerhein ). preferably , the rhein of formula ( v ) is prepared through steps a ), b &# 39 ;), b &# 34 ;) and c ) defined above and converted to the acyl derivative , preferably diacerhein , via step d ). treatment with the acylating agent as per step d ) is carried out at temperatures preferably ranging from about 50 ° c . to about 100 ° c ., e . g . from about 70 ° c . to 90 ° c . the acylating agent is , e . g ., the anhydride or acyl halide of the r b cooh acid , where r b is as defined above . the halide is typically used in the presence of a base as protons acceptor , and the anhydrides are used in the presence of an acid or basic catalyst ; the acid catalyst may be , e . g ., an organic acid , such as acetic acid , methanesulphonic acid , trifluoromethanesulphonic acid , or an inorganic acid , such as concentrated sulphuric acid , preferably h 2 so 4 ; the basic catalyst may be , e . g ., an organic base , typically an alkali metal acetate , such as sodium acetate , or an inorganic base , such as an alkali metal bicarbonate , e . g . nahco 3 . preferably , the acylating agent is acetic anhydride , an acetyl halide , such as the chloride , typically used in the presence of a base as a protons acceptor , or hexachloroacetone . acetic anhydride in the presence of an acid or basic catalyst is preferably used . the acylating agent ( typically acetic anhydride ) is generally in stoichiometric excess in respect of rhein , e . g . it amounts to from 2 . 0 to 5 . 0 mols , preferably 3 . 0 mols per mol of rhein . preferably , rhein is treated with acetic anhydride , in glacial acetic acid as reaction solvent , the solvent being in an amount ranging , e . g . from about 0 . 5 to about 5 ml , typically of about 1 ml per mmol of rhein , in the presence of a catalytic quantity of concentrated h 2 so 4 . diacerhein is easily isolated from the reaction medium as it precipitates by cooling to room temperature and is separated by conventional methods , such as filtration . the diphenylketone of formula ( ii ) is a novel product synthesized by the applicant from commercially available compounds . the derivative or - formula ( vii ) is obtained , e . g ., by oxidation of the dimethylbenzene derivative of formula ( xii ) ## str14 ## in which r 2 is a protective group of the -- oh function , preferably a saturated , straight or branched c 1 - c 4 alkyl group , with an oxidizing agent , preferably a hypochlorite ( such as nacl0 ), and with an alkyl halide , preferably containing 1 to 6 carbon atoms ( such as n - butylbromide ) , in the presence of a transition metal salt ( preferably a ru ( iii ) salt , such as rucl 3 ). preferably operating in an aqueous medium , at alkaline ph , at a temperature preferably ranging from 30 ° c . to 100 ° c ., preferably of about 40 ° c . to 60 ° c . the oxidation of the compound of formula ( xii ) is generally carried out in water , preferably at about ph 8 - 9 , this value being maintained by addition of a strong base , such as naoh . preferably , the oxidant used in respect of the dimethylbenzene derivative of formula ( xii ) amounts to from 2 to 5 mols , e . g . 3 mols ; the halide is preferably in a stoichiometric amount in respect of the derivative of formula ( xii ); the catalyst is typically in an amount ranging from 1 % to 30 % in mols , preferably from 10 % to 25 % in mols in respect of the derivative of formula ( xii ). several derivatives of formula ( xii ) are commercially available or may be prepared by conventional methods . preferred derivatives of formula ( vii ) above are the ones in which r 2 is a saturated , straight or branched c 1 - c 4 alkyl group , especially ch 3 . out of the derivatives of formula ( viii ), particularly preferred are the ones in which r 2 and r 3 , which may be the same or different one from the other , are c 1 - c 4 alkyl groups , preferably saturated , more particularly the ones in which r 2 = r 3 = ch 3 . in step 1 ), the temperature preferably ranges from about 30 ° c . to 100 ° c ., typically from about 50 ° c . to 70 ° c . furthermore , r 3 oh is preferably ch 3 oh and is preferably used as a reaction solvent , in an amount , e . g ., ranging from 0 . 5 to 2 ml , preferably of 1 ml per mmol of the derivative of formula ( vii ). preferably , the cu ( i ) salt is a halide , such as cucl , and the acid is an inorganic strong acid , typically a hydrogen halide , such as hcl ; furthermore , the cu ( i ) salt and the acid are preferably used in a stoichiometric amount in respect of the compound of formula ( vii ), as well as up to 2 mols per mol of ( vii ). preferred derivatives of formula ( ix ) are the ones in which r 2 and r 3 , which may be the same or different one from the other , are c 1 - c 4 alkyl groups , preferably saturated , and especially the ones in which r 2 = r 3 = ch 3 ; furthermore , hal is preferably cl or br and more preferably cl . the temperature of step 2 ) preferably ranges from about 50 ° c . to 120 ° c ., more preferably from about 60 ° c . to 90 ° c . ; the halogenating agent is , e . g ., thionyl chloride , pcl 5 or pcl 3 . typically , thionyl chloride is used , e . g ., as a reaction medium , in a quantity typically ranging from about 1 to 2 ml per 100 mmols of the derivative of formula ( viii ). the reaction is preferably carried out at the reflux temperature of the reaction mixture ( about 78 ° c . to 80 ° c .). step 2 ) may be also carried out in the presence of a diluent or of an inert organic solvent . preferred derivatives of formula ( x ) are the ones in which r 1 is -- or &# 39 ;, and r &# 39 ; and r4 , which may be the same or different one from the other , are preferably a saturated , straight or branched c 1 - c 4 alkyl , and more preferably the ones in which r 1 is -- och 3 and r 4 is ch 3 . the temperature of step 3 ) preferably ranges from about 40 ° c . to 100 ° c ., more preferably from about 40 ° c . to 60 ° c . furthermore , the catalyst is selected out of the catalysts commonly used in friedel - crafts reactions ( alkylations or acylations ) and is typically an aluminium halide , such as alcl step 3 ) preferably utilizes stoichiometric ratios of the derivative of formula ( x ) to the derivative of formula ( ix ) and amounts of friedel - crafts catalyst typically ranging from 0 . 1 % to 10 % in mols , more typically from about 1 % to 2 % in mols in respect of the derivative of formula ( ix ). according to a preferred embodiment of the present invention , step 3 ) is carried out in the absence of solvents , simply by mixing the substrates of formulas ( ix ) and ( x ) with the catalyst and raising the reaction temperature to the selected value . alternatively , however , step 3 ) may be also carried out in the presence of diluents or of inert organic solvents . preferred derivatives of formula ( xi ) are the ones in which r 1 is -- or &# 39 ;, and r , r 2 , r 3 and r 4 , which may be the same or different one from another , are preferably a saturated , straight or branched c 1 - c 4 alkyl , more preferably the ones in which r 1 is -- och 3 and r 2 = r 3 = ch 3 . in the hydrolysis ( step 4 ), the temperature preferably ranges from 30 ° c . to 100 ° c . and more preferably is of about 80 ° c . furthermore , the base is preferably an alkaline hydroxide , such as naoh , said base being used in a quantity preferably ranging from about 0 . 5 to 1 mol per mol of compound of formula ( xi ). step 4 ) is preferably carried out in a water - alcohol mixture , alcohol being , e . g ., methanol , ethanol , e . g . in 50 : 50 water / ethanol . at the end of the reaction , diphenylketone ( ii ) a is recovered from the reaction medium by acidification , typically with hcl . preferred derivatives of formula ( ii ) a are the ones in which r 2 is a c 1 - c 4 alkyl group , preferably saturated , and more typically r 2 = ch 3 . the derivatives of formula ( x ), in which r 1 is -- nr &# 39 ; r &# 34 ;, -- sr &# 39 ; or -- oh can be obtained from the corresponding derivatives , in which r 1 is -- or &# 39 ; as above defined , by conventional methods . the derivatives of formula ( x ), in which r 1 is -- or &# 39 ; as above defined , are e . g . prepared by esterification of 3 - aminobenzoic acid , followed by acylation of the aminic function . for example , 3 - aminobenzoic acid is treated with an r &# 39 ; oh alcohol , where r &# 39 ; is as defined above and is preferably a c 1 - c 4 alkyl group ( more preferably ch 3 ), in the presence of an acid catalyst , preferably at a temperature ranging from 30 ° c . to 100 ° c ., e . g . from 50 ° c . to 70 ° c . to give the corresponding ester of formula ( xiii ) ## str15 ## in which r &# 39 ; is as defined above and more preferably is ch 3 . r &# 39 ; oh is preferably ch 3 oh and is typically used as a reaction solvent ; furthermore , the acid catalyst is , e . g . concentrated h 2 so 4 , in a quantity ranging from 1 to 5 ml , e . g . 3 ml , per 100 mmols of substrate . the resulting derivative of formula ( xiii ) is treated with an acylating agent , preferably with the r 4 cooh acid anhydride . where r 4 is as defined above and is preferably a saturated c 1 - c 4 alkyl group , preferably in the presence of an acid catalyst . such as the r 4 cooh acid , at a temperature preferably ranging from about 80 ° c . to about 120 ° c . more preferably at about 100 ° c . to 120 ° c . preferably , r 4 is ch 3 , the anhydride is acetic anhydride and the acid is acetic acid , used , e . g . as reaction solvents , the acid . e . g ., in an amount of about 2 to 10 ml . preferably 5 ml . per 100 mmols of substrate of formula ( x ), and the anhydride in an amount of about 1 to 2 ml , e . g ., about 1 . 2 to 1 . 4 ml , per 100 mmols of substrate of formula ( xiii ). the compounds of formula ( x ) may be anyhow prepared by other conventional methods . the following examples are conveyed by way of indication , not of limitation , of the present invention . preparation of the intermediate of formula ( iii ) in which r 1 is -- oh and r 2 is -- ch 3 the intermediate of formula ( ii ) ( 0 . 01 mol ), in which r 5 is h , r 1 is -- oh and r 2 is -- ch 3 , was suspended in 30 ml concentrated strong acid , such as h 2 so 4 or cf 3 so 3 h , more preferably cf 3 so 3 h . the resulting mixture was heated to 150 ° c . for 2 hrs . under constant stirring . after said 2 hr - period , the solution was cooled to room temperature and neutralized with 10 % aqueous naoh . the precipitate was filtered , washed with water and evaporated to dryness , to give a crystalline product corresponding to the intermediate of formula ( iii ) ( 0 . 0089 mol ), in which r 1 is -- oh and r 2 is -- ch 3 . total yield 88 %. melting point 226 ° c . the product was analysed by tlc on silica gel and identified by ir spectrometry . preparation of the intermediate of formula ( iv ) in which r 2 is -- ch 3 the intermediate of formula ( iii ) ( 0 . 01 mol ), in which r 1 is oh and r 2 is -- ch 3 , obtained as per example 1 . was dissolved in a 1 : 3 sulphuric acid / water mixture ( v / v ), in a quantity of about 20 to 35 ml . the resulting mixture was cooled to 0 ° c . to 5 ° c ., allowed to stir until complete dissolution of the intermediate of formula ( iii ), and added with nano 2 ( 0 . 015 mol ) dissolved in 10 ml cool water ( 50 ° c .). the reaction mixture was left under stirring for an additional 15 min . and added with 100 ml of a 1 : 1 water - sulphuric acid mixture ( v / v ). the solution was heated to 150 ° c . for 1 hr . under constant stirring . after cooling to room temperature , the resulting precipitate was collected by filtration in vacuo , washed with water and dried under reduced pressure at 50 ° c . a yellow - brown crystalline solid was obtained ( m . p . 261 ° c .). corresponding to the intermediate of formula ( iv ) ( 0 . 0085 mol ) in which r 2 is -- ch 3 . the product obtained as per example 2 [ intermediate of formula ( iv ) in which r 2 is -- ch 3 ] was suspended in 100 ml glacial acetic acid containing a 48 % hbr solution in water ( 10 ml ). the reaction mixture was heated to reflux for 3 hrs ., cooled to room temperature and filtered . the precipitate obtained was collected by filtration in vacuo , washed with water and dried under reduced pressure . recrystallization from methanol gave a yellow - greenish needle - shaped product ( m . p . 244 ° c . to 246 ° c .). yield 79 % to 83 %. elemental analysis , ir and rf values are in accordance with the values found for rhein [ compound of formula ( v )]. rhein ( 0 . 01 mol ) obtained as per example 3 was suspended in 100 ml glacial acetic acid . the resulting suspension was added with acetic anhydride ( 0 . 03 mol ) and one drop of concentrated sulphuric acid . and heated to 80 ° c . under stirring for 1 hr . the solution was allowed to cool to room temperature . a yellow - greenish precipitate was collected by filtration in vacuo , washed with water and dried under reduced pressure . total yield 98 %. melting point 247 ° c . ir spectrum : v max 1733 cm - 1 ( ester ), 1701 cm - 1 ( carboxyl ), 1689 cm - 1 ( carbonyl ). elemental analysis : calcd for c 19 h 12 o 8 : c , 61 , 96 ; h . 3 . 29 ; found : c , 62 . 07 ; h 3 . 39 . the above data prove that the product obtained is identical with an authentic diacerhein sample . diphenylone of formula ( ii ) a in which r 2 is -- ch 3 preparation of methoxyphthalic acid [ derivative of formula ( vii ) in which r 2 is ch 3 ] a mixture was made up as follows : 0 . 1 mol of 2 , 3 - dimethylmethoxybenzene [ derivative of formula ( xii ) in which r 2 is ch 3 ], added with 0 . 3 mol of naclo , as an aqueous solution containing 15 % active cl ; n - butylbromide ( 0 . 1 mol ); rucl 3 . 3h 2 o ( 0 . 02 mol ). the mixture was vigorously stirred at 50 ° c . and the ph of the solution was maintained at 8 - 9 through the addition of 2m naoh . when the ph of the solution remained constant , the reaction mixture was allowed to stir for an additional 1 hr ., cooled to room temperature and acidified with a concentrated hcl - h 2 o mixture until complete precipitation of methoxyphthalic acid . the precipitate was collected by filtration and dried under reduced pressure . the methoxyphthalic acid yield was 98 %. preparation of methoxyphthalic acid monomethylester [ derivative of formula ( viii ) in which r 2 = r 3 = ch 3 ] a solution of methoxyphthalic acid obtained as per example 5 ( 0 . 1 mol ) in 100 ml methanol was added with cucl ( 0 . 1 mol ) and hcl ( 0 . 1 mol ). the solution was heated to reflux for 30 min . the clear solution obtained was evaporated to dryness under reduced pressure . the residue obtained was dissolved in a 1 : 3 water - methanol mixture and acidified . the product was separated by cooling , collected by filtration and air dried . the product yield was 63 - 66 %. preparation of methoxyphthalic acid monomethylester chloride [ derivative of formula ( ix ) in which r 2 = r 3 = ch 3 and hal is cl ] the methoxyphthalic acid monomethylester obtained as per example 6 ( 0 . 1 mol ) was suspended in thionyl chloride ( 1 . 5 ml ). the resulting suspension was slowly heated to reflux until complete dissolution of the solid material . after refluxing for an additional 30 min ., excess thionyl chloride was removed under reduced pressure and the residue was recrystallized from toluene . a ) preparation of 3 - aminobenzoic acid monomethylester [ derivative of formula ( xiii ) in which r 1 is -- och 3 ] 3 - aminobenzoic acid ( 0 . 1 mol ) was added with 50 ml methanol . the mixture was cooled in an ice bath and slowly added with 3 ml concentrated h 2 so 4 . the components were mixed and refluxed for 1 hr . the solution was cooled , settled in a separatory funnel containing 50 ml water . the vessel was fed with 35 ml t - butylmethylether . after mixing , the aqueous layer was removed and the ethereal phase was washed first with 25 ml water and then with 25 ml 1 . 5m nahco 3 . the ethereal phase was evaporated under an aspirating tube . b ) preparation of 3 - aminobenzoic acid monomethylester n - acetyl derivative [ derivative of formula ( x ) in which r 1 is -- och 3 and r 4 is ch 3 ] the 3 - aminobenzoic acid monomethylester obtained as per a ) above ( 0 . 1 mol ) was added with acetic acid ( 5 ml ). the resulting mixture was heated slightly above 100 ° c . and the solution was allowed to stir . the temperature was allowed to decrease to 100 ° c . and acetic anhydride ( 1 . 3 ml ) was added . the mixture was left under stirring until the temperature lowered to 75 ° c . and water ( 1 ml ) was added . water was removed in vacuo and the resulting oily syrup was resuspended in cyclohexane ( 5 ml ). the temperature was raised to remove the trace water from the syrup as a cyclohexane - water azeotrope . the title product yield was 89 % to 93 %. preparation of diphenylketone of formula ( xi ) in which r 1 is -- och 3 and r 2 = r 3 = r 4 = ch 3 methoxyphthalic acid monomethylester chloride ( 0 . 1 mol ) and 3 - aminobenzoic acid monomethylester n - acetyl derivative were caused to react in a 10 × 100 mm tube . the reaction mixture was cooled in an ice bath and added with anhydrous alcl 3 ( 200 mg ). the tube was sealed with a septum connected with a teflon tube immersed in a moist cotton plug trapping the hcl being developed during the reaction . the tube content was carefully mixed and cautiously heated in a hot water vessel . gaseous hcl evolution was controlled by repeatedly heating and cooling the reaction mixture . the reaction was continued for about 15 min . at 50 ° c . until gas evolution ceased completely . the mixture was cooled in an ice bath and added with ice in small pieces ( 1 g ). each piece of ice was allowed to react before adding the successive piece . the tube content was carefully mixed , cooled to room temperature , added with 0 . 5 ml water and 5 ml t - butylether , and mixed . the aqueous phase was removed . once extraction had been repeated , concentrated hcl ( 0 . 2 ml ) in 0 . 5 ml water was added . the organic layer was transferred into a small test tube and evaporated to dryness . hydrolysis of diphenylketone of formula ( xi ), in which r 1 is -- och 3 , r 2 = r 3 = r 4 = ch 3 , to give the dimethylketone of formula ( ii ) a , in which r 2 is ch 3 the diphenylketone obtained as per example 9 ( 0 . 1 ml ) was treated with a 50 : 50 water - ethanol mixture ( 3 ml ) containing naoh ( about 1 . 89 to 3 . 6 g ). the mixture was cautiously heated to reflux in a sand bath for 30 min . once the reaction had been completed , the solution was acidified , the precipitate was collected by filtration , and air dried . the product yield was 90 %.