PYRROLE AND ITS DERIVATIVES 305 



Pyrrole. C 4 H 5 N. 



Pyrrole was found in coal tar in 1834 an< ^ m bone oil in 1858 and 

 is usually obtained from bone oil. 



Preparation. 



The oil which is obtained by the dry distillation of bones contains 

 pyridine and basic substances, aromatic hydrocarbons, pyrrole and its 

 homologues, but consists mainly of the nitriles of fatty acids. The basic 

 substances are removed by agitation with dilute acid, the nitriles are 

 hydrolysed by boiling with alkali and the oil which remains is fractionally 

 distilled. The fraction passing over between 115 and 130 contains the 

 pyrrole. By boiling with solid caustic potash it is converted into solid 

 potassium pyrrole, C 4 H 4 NK, which is filtered off and decomposed by water. 

 The pyrrole is then isolated by distillation. 



Fat-free bone gelatin is said to give a distillate consisting mainly of 

 pyrrole and its homologues. 



It is probably formed from the proline and hydroxyproline contained in 

 the protein, but may also arise by the dry distillation of glutamic acid. 



It has been synthesised by passing acetylene and ammonia through red- 

 hot tubes, by the dry distillation of the ammonium salt of mucic acid and by 

 the reduction of succinimide by distillation- over zinc dust: 

 CH 2 CCK CHCH. 



>NH + 2H 2 = I >NH + 2 H 2 0. 



CH 2 CO/ CH=CH/ 



Properties. 



Pyrrole is a colourless liquid smelling like chloroform but turning 

 brown in the air. It boils at 131, is very slightly soluble in water, 

 but is easily soluble in alcohol and ether. 



Pyrrole is a secondary amine and has a slight basic character ; it 

 dissolves slowly in dilute acids and is converted into a resin by strong 

 acids. Its solution in dilute acids on warming deposits a red precipi- 

 tate termed pyrrole red. 



It gives a fiery red colour with a pine shaving moistened with 

 hydrochloric acid. Hence its name from irvppo^ 



As a secondary amine pyrrole forms a nitroso compound with 

 sodium ethoxide and amyl nitrite. 



Potassium dissolves in pyrrole with evolution of hydrogen. The 

 combination of pyrrole with potassium to form solid potassium pyrrole 

 is probably due to the acid influence of the CH groups. 



The pyrrole ring is easily ruptured. Succinyl dialdoxime is formed by 

 the action of hydroxylamine upon pyrrole. a-substituted pyrroles yield 

 ketoximes, ^-substituted pyrroles yield aldoximes from which dibasic acids can 

 be obtained. This reaction serves for determining the position of substituting 

 groups. 



Pyrrole reacts violently with halogens ; but derivatives are obtained by 

 using dilute solutions. Tetraiodopyrrole, which is prepared by the action of 

 iodine on pyrrole in the presence of alkali, forms yellow-brown prisms which 

 melt at 140. Under the name of iodol it is used as an antiseptic and has 

 an advantage over iodoform in possessing no smell. 



