GUANIDINE AND ITS DERIVATIVES 169 



Creatinine. 



Creatinine is present in all mammalian urines. The amount of 

 creatinine in human urine varies from about 075-1-5 gm. per diem. 

 It is not present in muscle or it is present only in traces. It has been 

 found in wheat, rye and other crops and has been isolated from 

 cultivated soil. 



Creatinine is present in meat extracts. Its presence is probably 

 due to the action of the acids of muscle extracts upon creatine during 

 evaporation. 



Preparation. 



Creatinine is obtained from creatine by boiling with acids. It is 

 most conveniently prepared from human urine by Folin's method and 

 it is advantageous to use as large quantities of fresh^ not ammoniacal, 

 urine as possible. 



60-80 gm. of picric acid (i.e. 6-8 gms. per litre of urine) are dissolved 

 in 400 c.c. of hot alcohol and are added with stirring to 8 litres of urine. 

 The double picrate of creatinine and potassium is precipitated. After the 

 mixture has stood for 12-24 hours the liquid is decanted or syphoned off 

 and the precipitate drained and washed with cold water on a Buchner funnel. 



100 gm. of dry potassium carbonate and 750 c.c. of water are added 

 to 500 gm. of dry picrate, the mixture is thoroughly stirred for 10 minutes 

 and allowed to stand for 1-2 hours. The precipitate is filtered off on 

 a Buchner funnel and the sediment washed two or three times with small 

 quantities of water. The filtrate containing the creatinine is transferred to 

 a large jar and 100 c.c. of 99 per cent, acetic acid (i c.c. per gm. of carbonate) 

 are added in such a way that it drops upon the foam which is formed and 

 breaks it up. The acid solution which is wine-red in colour is treated with 

 one-fourth of its volume of a concentrated alcoholic zinc chloride solution. 1 

 A large precipitate of creatinine zinc chloride is formed at once, if sufficient 

 zinc chloride has been added, and is filtered off. 



This double salt is decomposed by lead hydroxide which must be freshly 

 precipitated and is prepared from lead nitrate. 4-5 gm. of lead nitrate 

 per gm. of creatinine zinc salt are dissolved in 7-8 parts of cold water and 

 precipitated by adding 2 c.c. of strong ammonia per gm. of nitrate. The 

 lead hydroxide settles rapidly, the liquid is syphoned off, and the hydroxide 

 washed three times with large quantities of water. 



The creatinine zinc chloride is placed in 30 parts of water previously 

 heated to boiling and contained in a flask filled not more than two-thirds, and 

 again heated to boiling so as to dissolve as large a portion as possible. The 

 lead hydroxide in suspension in water is added in portions of about one-fifth 

 of the requisite quantity and the mixture is boiled after each addition. The 

 solution is boiled for half to one hour after all the hydroxide has been added 

 so that the precipitate becomes granular, cooled and filtered. The filtrate 

 should be clear, but if not clear may be treated with hydrogen sulphide and 

 again filtered. The filtrate is freed from lead by hydrogen sulphide and eva- 

 porated to dryness. The dry residue consists of creatinine and creatine. It 



1 One part of zinc chloride dissolves in about one part of alcohol ; a sediment of zinc 

 hydroxide may be brought into solution by adding a few drops of hydrochloric acid. 



