Patent Abstract:
the present invention provides a process for preparing of 2 - acetyl - 1 - pyrroline , the principle aroma component of basmati and other varieties of scented rice , and also of processed cereal and grain products , said flavor chemical is of great value , in the art of application of flavor to foodstuffs like rice and bakery products .

Detailed Description:
in accordance to the objectives , the present invention provides a process for the preparation of 2 - acetyl - 1 - proline , the said process comprising steps of : a ) dissolving l - pyrroline in dry alcohol , cooling to a temperature in the range of − 5 ° c . to − 15 ° c ., b ) adding thionylchloride to step ( a ) solution , maintaining the temperature of reactant mixture below 0 ° c ., c ) stirring the reactant mixture of step ( b ) at a temperature range of 20 ° to 30 ° c . for a time period of 1 h to 4 h , d ) removing the solvent from reactant mixture of step ( c ) to obtain a residue , which is stored in ice - chest for a time period of 10 hours to 16 hours to obtain a solid mass , e ) adding the solid mass of step ( d ) to 50 % aqueous alkali carbonate solution , extracting with an organic solvent , separating the organic and aqueous layer , f ) drying the organic layer of step ( e ) over anhydrous sodium sulphate , filtering , evaporating the solvent from filtrate to obtain a residue , h ) dissolving 2 - carbomethoxy - 1 - pyrrolidine of step ( g ) in ether , cooling to a temperature range of 0 ° to 5 ° c ., adding drop wise t - butylhypochlorite over a period of 10 minutes to 30 minutes , stirring at a temperature range of 20 ° to 30 ° c . for a time period of 4 h to 6 h , i ) filtering the solution of step ( h ), removing the solvent from the filtrate to obtain 2 - carbomethoxy - 1 - pyrroline , j ) preparing grignard reagent in dry ether by adding magnesium turning , iodine followed by dropwise methyl iodide and stirring at a temperature in the range of 25 ° c . to 35 ° c . for completion of reaction , cooling the mixture to 0 ° c ., k ) adding an ethereal solution of 2 - carbomethyoxy - 1 - pyrroline to the cooled mixture of step ( j ), stirring at a room temperature till the reaction is complete , i ) adding 5 % aqueous hydrochloric acid to step ( k ) mixture , extracting with diethyl ether , separating the organic layer , drying the organic layer over anhydrous sodium sulphate , filtering to obtain a filtrate , and j ) distilling the filtrate of step ( i ) to obtain pure 2 - acetyl - 1 - pyrroline . in an embodiment of the invention relates to use of dry alcohol , which is selected from a group consisting of dry methanol , ethanol and propanol , preferably methanol . another embodiment , the organic solvent used is selected from a group consisting of dimethyl ether , diethyl ether and di - isopropyl ether , preferably diethyl ether . another embodiment , the aqueous alkali carbonate solution used , is selected from a group consisting of 50 % aqueous sodium carbonate or 50 % aqueous potassium carbonate . still another embodiment , the dehydrogenation can be performed using potassium acetate . still another embodiment , the 2 - acetyl - 1 - pyrroline obtained has a basmati rice flavor or popcorn flavor . still another embodiment , the 2 - acetyl - 1 - pyrroline obtained is used in flavoring agent in food products , bakery products , food drinks and rice products . in an embodiment of the present invention , proline was converted to 2 -( carbomethoxy ) pyrrolidine by reaction with thionyl chloride under mild conditions . in yet another embodiment of the invention , 2 -( carbomethoxy )- n - chloropyrrolidine was dehydrohalogenated by reaction with potassium t - butoxide or potassium acetate at ambient temperatures . in another embodiment of the present invention , 2 -( carbomethoxy )- 1 - pyrroline was converted to 2 - acetyl - 1 - pyrroline by a known grignard reaction with methylmagnesium iodide . the following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention . a solution of l - proline ( 2 . 23 g ) in dry methanol ( 15 ml ) was cooled to − 5 ° c . and thionyl chloride ( 4 . 52 g ) was added dropwise , while stirring and maintaining the temperature of the reactants below 0 ° c . the reaction was continued at 25 ° c . for 2 h . the solvent was distilled and the residue stored in ice - chest for 12 h . the solid mass was added to aqueous solution of potassium carbonate ( 50 %, 20 ml ) at 0 ° c . and the separated oily layer was extracted into ether ( 15 ml × 3 ). the ethereal layer was dried over anhydrous sodium sulfate and distilled to afford 2 . 3 g of 2 -( carbomethoxy )- pyrrolidine ( 85 %), [ ms ( m / z ) m + 129 ( 1 %), 114 ( 0 . 5 ), 70 ( 100 ), 68 ( 50 ), 43 ( 80 ), 41 ( 90 )]. it was taken in dry diethyl ether ( 15 ml ), cooled to 0 ° c . and t - butylhypochlorite ( 2 . 16 g ) added dropwise . the reaction was monitored on silica gel thin layer using chloroform as the eluant . after completion of the reaction ( 15 min . ), potassium t - butoxide ( 2 . 24 g ) was added gradually over 10 min . and the reactants stirred at 25 ° c . for 5 h . the solution was filtered and the solvent distilled under reduced pressure to afford 2 -( carbomethoxy )- 1 - pyrrroline ( 2 g ), [ ms ( m / z ) m + 127 ( 1 %), 112 ( 0 . 5 ), 97 ( 15 ), 69 ( 100 ), 54 ( 50 ), 41 ( 75 )]. to a suspension of magnesium turnings ( 0 . 43 g ) in dry ether , iodine ( 0 . 01 g ) was added followed by dropwise addition of a solution of methyl iodide ( 3 . 08 g ) in ether ( 5 ml ) at 35 ° c . the mixture was stirred until the disappearance of magnesium turnings ( 15 min ), then cooled to 0 ° c . to it , a solution of 2 -( carbomethoxy )- 1 - pyrrroline ( 2 g ) in dry ether ( 5 ml ) was added over 5 min . and the mixture was stirred at room temperature . on completion of the reaction ( 2 h ) the product was worked up by the addition of dilute hydrochloric acid ( 5 %, 10 ml ) and the organic layer separated . the aqueous layer was further extracted with ether ( 10 ml × 2 ) and the combined organic layers dried over anhydrous sodium sulphate and distilled to afford pure 2 - acetyl - 1 - pyrroline [ 1 . 3g , 95 % purity , ms ( m / z ) m + 111 ( 5 %), 96 ( 0 . 1 ), 83 ( 15 ), 69 ( 8 ), 68 ( 10 ), 55 ( 2 ), 52 ( 0 . 2 ), 43 ( 100 ), 42 ( 25 ), 41 ( 50 )]. to a solution of l - proline ( 2 . 23 g ) in dry methanol ( 15 ml ) cooled to − 5 ° c ., thionyl chloride ( 4 . 52 g ) was added drop wise , while stirring and maintaining the temperature of the reactants below 0 ° c . the reaction mixture was allowed to attain room temperature ( 25 ° c .) and further stirred for 2 h . the solvent was distilled off from it and the residue stored in ice - chest for 12 h . the solid mass that separated was added to an aqueous potassium carbonate solution ( 50 %, 20 ml ) at 0 ° c . and the separated oily layer extracted into ether ( 15 ml × 3 ). the combined ethereal layers were dried over anhydrous sodium sulfate and distilled to afford 2 . 3 g of 2 -( carbomethoxy )- pyrrolidine [ 85 %, ms ( m / z ) m + 129 ( 1 %), 114 ( 0 . 5 ), 70 ( 100 ), 68 ( 50 ), 43 ( 80 ), 41 ( 90 )]. to an ice - cooled solution of the compound in dry diethyl ether ( 15 ml ), t - butylhypochlorite ( 2 . 16 g ) was added drop - wise . the reaction was monitored on thin layer of silica gel using chloroform as the eluant . after 15 min . anhydrous potassium acetate ( 2 . 76 g ) was added gradually added to it over 10 min ., and the mixture stirred at 25 ° c ., while monitoring the reaction by tlc . at the end of the reaction ( 3 h ), the solution was filtered and the solvent distilled under reduced pressure to afford 2 - carbomethoxy )- 1 - pyrrroline [ yield : 1 . 9 g , ms ( m / z ) m + 127 ( 1 %), 112 ( 0 . 5 ), 97 ( 15 ), 69 ,( 100 ), 54 ( 50 ), 41 ( 75 )]. to a suspension of magnesium turnings ( 0 . 43 g ) in dry diethylether , iodine ( 0 . 01 g ) was added followed by a solution of methyl iodide ( 3 . 08 g ) in ether ( 5 ml ) dropwise at 35 ° c . the mixture was stirred until the disappearance of magnesium ( 15 min ) and then after cooling to 0 ° c ., a solution of 2 -( carbomethoxy )- 1 - pyrrroline ( 1 . 9 g ) in dry diethylether ( 5 ml ) was added over 5 min . on completion of the reaction ( 2 h ) as found by gc , the product was worked up by addition of dilute hydrochloric acid ( 5 %, 10 ml ) and separation of the organic layer . the aqueous layer was further extracted with diethylether ( 10 ml × 2 ) and the combined organic layers dried over anhydrous sodium sulphate . removal of the solvent afforded pure 2 - 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