352 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Most alkaloids give precipitates with the following reagents : 



(1) tannic acid ; 



(2) picric acid ; 



(3) iodine in potassium iodide ; 



(4) mercuric iodide in potassium iodide ; 



(5) phosphotungstic acid and phosphomolybdic acid. 



These reagents, termed alkaloidal reagents, also give precipitates 

 with amines and other bases and with proteins. They cannot in 

 consequence be considered as specific for the alkaloids, but they are 

 sometimes useful for isolating and detecting alkaloids. 



Piperine. 



Piperine is found in the fruit of the various varieties of pepper ; about 8 

 or 9 per cent, is present in black pepper. 



Powdered pepper is warmed with lime water for 15-20 minutes and the 

 mixture is evaporated to dryhess. The dry residue is extracted with ether. 

 The ethereal solution on distillation leaves piperine, which is purified by 

 crystallisation from alcohol. 



Piperine is a white solid which melts at 128. It is almost insoluble in 

 water. It behaves as a weak base and dissolves in concentrated sulphuric acid 

 giving a deep red solution. 



Constitution. 



On distillation with alcoholic potash, piperine is converted into piperidine 

 and piperic acid. Piperine is the amide of piperidine and piperic acid. It 

 has been synthesised by the action of piperic acid chloride on piperidine. 

 /CIV-CH, ' 

 CH 2 \N . OC . CH =CH . CH= CH 



Nv CH 2 CH a 



Piperine. 

 >CH 2 . CH 2 



CH 2 \NH + HOOC.CH=CH ,CH=CH 



^CH a . CH 2 



Piperidine. Piperic acid or 



3, 4 methylene dihydroxycinnamenyl- 

 acrylic acid. 



Coniine. C 8 H l7 N. 



Coniine is the alkaloid which is present in the seeds of hemlock. 

 It is prepared therefrom by distillation with sodium hydroxide. 



Coniine is a colourless liquid which boils at 167. It has a 

 peculiar and penetrating odour and turns brown in the air. It is 

 soluble in water and is a strong base forming salts with acids. 



The natural substance is optically active and dextrorotatory. 



Constitution. 



Coniine has been shown to be a-propylpiperidine and has been 

 synthesised as follows : 



/\ 



heat 



