all patents , patent applications , and publications disclosed herein are hereby incorporated by reference in their entirety . in case of a conflict in terminology , the present specification controls . generally , the first step of the process of the present invention comprises the condensation of n - pentylamine with benzaldehyde to produce the n - benzylidene - n - pentylamine of formula ii . this condensation can be carried out in a suitable solvent such as aliphatic alcohols , at a reaction temperature of 40 ° c . to 90 ° c ., for example in methanol at 70 ° c . to 75 ° c . typically , the second step of the process of the present invention comprises the transformation of the n - benzylidene - n - pentylamine into the n - methyl - n - pentylamine with a methylating agent . methylating agents such as methyl halogenides or dimethyl sulfate can be employed , but preferably dimethyl sulfate is used . the reaction can be conducted at a temperature of 80 ° c . to 110 ° c ., preferably at 90 ° c . to 100 ° c . the benzaldehyde that is generated can be removed , for example , by steam distillation and the resulting n - methyl - n - pentylamine can be isolated from the aqueous phase by any means known to the skilled in the art such as by addition of a base and extraction of the basic solution with a suitable organic solvent such as an aliphatic ether , for example with diisopropylether . the product can be further purified , for instance , by distillation . generally , a third step of the process of the present invention involves reacting the n - methyl - n - pentylamine with methyl acrylate to form the n - methyl - n - pentyl - β - alanine methylester of formula iii . this reaction can be carried out in a suitable solvent such as an aliphatic alcohol , an aliphatic ether or an ether / alcohol mixture , for example in methanol at a reaction temperature of 10 ° c . to 65 ° c ., or at 15 ° c . to 25 ° c . isolation of the n - methyl - n - pentyl - β - alanine methyl ester can be performed by techniques known to the skilled in the art such as by distillation . hydrolysis of the n - methyl - n - pentyl - β - alanine methyl ester and formation of the hydrohalogenide produces the compound of the formula iv . the hydrolysis can be performed by refluxing the n - methyl - n - pentyl - β - alanine methyl ester in a diluted mineral acid , but can also be performed by refluxing in water at least until no ester can be detected any further . formation of the hydrohalogenide such as the hydrobromide or the hydrochloride , preferably of the hydrochloride ( x ═ cl ) can be effected by addition of an aqueous solution of the appropriate mineral acid . the resulting n - methyl - n - pentyl - β - alanine hydrohalogenide , e . g ., hydrochloride , can be isolated by distilling of the water and by a crystallization of the residue in a suitable solvent such as toluene / acetone or methyl ethyl ketone , preferably in methyl ethyl ketone . bisphosphorylating the compound of formula iv by means of phosphoryl chloride and phosphorous acid yields ibandronic acid , which can then be treated with the appropriate base to yield the monosodium salt , monohydrate . the bisphosphorylation of the n - methyl - n - pentyl - β - alanine hydrochloride may take place either in the presence of a non aromatic solvent or with no solvent present . it is preferred to use a non aromatic solvent . suitable non aromatic solvents are , for example , phosphoric acid esters , phosphonic acid esters or carbonic acid esters . a preferred solvent is diethylcarbonate . as phosphorylating agent a mixture of phosphoryl chloride and phosphorous acid is used . the molar ratio n - methyl - n - pentyl - β - alanine hydrochloride / phosphoryl chloride / phosphorous acid can range between 1 : 3 : 3 to 1 : 1 . 4 : 2 . 4 , preferably 1 : 1 . 6 : 2 . 4 to 1 : 1 . 4 : 2 . 4 during the bisphosphorylation the reaction temperature is typically maintained in a range of from 60 ° c . to 100 ° c ., preferably 80 ° c . to 90 ° c . in case a non aromatic solvent is used it can be removed , for example , by addition of water and subsequent azeotropic distillation . in order to isolate the monosodium salt , monohydrate of the 3 -( n - methyl - n - pentyl ) amino - 1 - hydroxypropane - 1 , 1 - diphosphonic acid the ph of the remaining aqueous reaction mixture is adjusted to a ph from about 3 . 5 to 6 , preferably from 4 . 4 to 4 . 5 with an aqueous solution of a sodium - containing base , such as sodium hydroxide , at a temperature in the range of about 20 ° c . to 25 ° c . the ibandronate sodium so obtained can be crystallized in suitable solvents such as aliphatic alcohols / water or aliphatic ketones / water , preferably in ethanol / water and acetone / water . a further object of the present invention is to provide a process for the preparation of 3 -( n - methyl - n - pentyl ) amino - 1 - hydroxypropane - 1 , 1 - diphosphonic acid , monosodium salt , monohydrate of the formula i by reacting the compound of formula iv with phosphoryl chloride and phosphorous acid and subsequently forming the monosodium salt , monohydrate . the preferred embodiments of this bisphosphorylation process are described above in paragraphs [ 17 ] to [ 22 ]. the process of the present invention allows the production of 3 -( n - methyl - n - pentyl ) amino - 1 - hydroxypropane - 1 , 1 - diphosphonic acid , monosodium salt , monohydrate of the formula i in excellent yield and quality . 100 g ( 1 . 15 mol ) n - pentylamine was added to 200 ml methanol at a temperature of 22 ° c . 121 . 8 g ( 1 . 15 mol ) benzaldehyde was added . the mixture was refluxed and subsequently , methanol was distilled off . the residual n - benzylidene - n - pentylamine 199 . 8 g ( 99 . 4 %) was used in the next step . 60 g ( 475 . 7 mmol ) dimethyl sulfate and 67 g ( 382 . 2 mmol ) n - benzylidene - n - pentylamine were stirred at a temperature of 90 – 100 ° c . and 117 ml purified water was added to the mixture . the generated benzaldehyde was removed by steam distillation . 133 ml diisopropyl ether and 54 ml sodium hydroxide solution ( 50 %) were added . the aqueous layer was separated . diisopropyl ether was distilled off . 3 . 3 g sodium hydroxide flakes are added to the residue to bind residual water . the residue , crude n - methyl - n - pentylamine was purified by distillation ( 29 . 4 g ; 76 %). 106 g ( 1 . 05 mol ) n - methyl - n - pentylamine was added to cooled methanol of a temperature of 0 – 5 ° c . 108 g ( 1 . 25 mol ) methyl acrylate was added to the solution and the mixture was stirred at room temperature for 8 hours . then methanol was distilled off in vacuo and the residue was purified by distillation to obtain 188 . 6 g n - methyl - n - pentyl - β - alanine methyl ester ( 96 . 1 %) 68 . 8 g ( 367 . 4 mmol ) n - methyl - n - pentyl - β - alanine methyl ester was hydrolyzed by refluxing with 138 ml water . then the water is partly distilled off and 83 ml ( 472 . 7 mmol ) hydrochloric acid ( 19 %) was added . water was distilled off again and 230 ml methyl ethyl ketone was added to remove residual water by azeotropic distillation . the reaction mixture was then cooled to 24 ° c . the crystallized product was separated and washed with methyl ethyl ketone and subsequently dried in vacuo . 63 . 7 g ( 82 . 7 %) n - methyl - n - pentyl - β - alanine hydrochloride were obtained . e1 ) preparation of 3 -( n - methyl - n - pentyl ) amino - 1 - hydroxypropane - 1 , 1 - diphosphonic acid , monosodium salt , monohydrate , in presence of diethyl carbonate as diluent 250 g ( 1 . 19 mol ) n - methyl - n - pentyl - β - alanine hydrochloride , 233 g ( 2 . 84 mol ) phosphorous acid , 151 ml ( 1 . 65 mol ) phosphoryl chloride and 900 ml diethylcarbonate were heated stepwise to 80 ° c . after 2 hours reaction time under continued heating the mixture was cooled to 60 ° c . and 1733 ml water were added , followed by azeotropic distillation of diethylcarbonate / water at 90 to 101 ° c . 358 ml water was added , the mixture was refluxed and water was distilled off . 316 ml water were added and water was distilled off twice . finally 2040 ml water were added and the residue was cooled to 24 ° c . the ph was adjusted at 23 ° c . with sodium hydroxide solution ( 50 %) to 4 . 4 . thereafter , 1100 ml ethanol were added to start crystallization . the suspension was stirred for 8 hours at 21 to 22 ° c . then the solid was separated , washed with 344 ml cold ethanol / purified water ( 7 / 5 v / v ), subsequently with 344 ml acetone / purified water ( 5 / 2 v / v ) and dried at 60 ° c . 315 . 6 g ( 73 . 7 %) of the title product were obtained in the form of colorless crystals . 36 . 3 g ( 172 . 8 mmol ) n - methyl - n - pentyl - β - alanine hydrochloride , 33 . 9 g ( 413 . 2 mmol ) phosphorous acid , 22 . 75 ml ( 248 . 6 mmol ) phosphoryl chloride were heated stepwise to 80 ° c . after 2 hours reaction time under continued heating the mixture was cooled to 60 ° c . and 251 , 7 ml water were added . the mixture was refluxed and water was distilled off . 46 ml water were added and water was distilled off twice . 296 . 5 ml water were added and the residue was cooled to 24 ° c . the ph was adjusted with sodium hydroxide solution ( 50 %) to 4 . 5 at 23 ° c . thereafter , 159 , 7 ml ethanol were added to start crystallization . the suspension was stirred for 8 hours at 21 – 22 ° c . then the solid was separated , washed with 90 ml cold ethanol / purified water ( 3 / 2v / v ), subsequently with 90 ml acetone / purified water ( 5 / 2 v / v ) and dried at 60 ° c . 42 . 6 g ( 68 . 6 %) of the title product were obtained in the form of colorless crystals .