106 Proceedings of the Royal Irish Academy. 



If the last formula correctly represented the constitution of the tetra- 

 hydropyrone, then this substance should be obtained by the action of 

 benzaldehyde on the a-benzylidene derivative of methyl-ethyl-ketone. 



In conjunction with Miss A. Devine one of us showed (Proc. Eoyal Irish 

 Acad., 1916. xxxii. B. p. 211) that in the presence of alkali benzaldehyde 

 condenses with methyl-ethyl-ketone to form o-benzylidene-methyl-ethyl- 

 ketone, CeHj. CH : CH . CO . CH3, which condenses further with benzaldehyde 

 in the presence of alcoholic hydrochloric acid to yield a compound CjsIIjoO 

 melting at 156' C. and quite different in composition and properties from the 

 tetrahydropyrone which was expected. It was obvious therefore that 

 «-benzylidene-methyl-ethyl-ketone cannot, as Eyan and Dunlea assumed, be 

 an intermediate product in the formation of the tetrahydropyrone and that 

 further investigation of the course of the reaction was necessary. 



Since methyl-ethyl-ketone, a product of the hydrolysis of monomethyl- 

 aeetylacetone, on condensation with benzaldehyde in the presence of alcoholic 

 hydrochloric acid formed a substance differing from the benzylidene derivative 

 of the tetrahydropyrone, it remained to find how methyl-isopropyl-ketone, a 

 product of the hydrolysis of dimethyl-acetylacetone, would behave under 

 similar conditions. 



We found that methyl-isopropyl-ketone and benzaldehyde in the presence 

 of alcoholic hydrochloric acid condense to form, in good yield, the benzylidene 

 derivative of the terahydropyrone obtained by Eyan and Dunlea from 

 benzaldehyde and dimethyl-acetylacetone 



This result showed that the formula CjsHsjOa, attributed to the 

 tetrahydropyrone derivative by Eyan and Dunlea, must be replaced by 

 CisHjjOj, and also corresponding formulae must be assigned to the hydro- 

 chloride CaHasOjCl, the dibromide CtsHjiOaBrj, and the hydroxy lamine 

 derivative CosH.sOs'NHOH of this substance, and with which the analytical 

 results already published {loc. cit.) agree as well as, if not better than, with 

 the formulae derived from C^HsjOj. The preparation of the tetrahydropyrone 

 derivative may now be formulated in the following manner : — 



aUjCHO + CH3 . CO . CH(CH3). = CeH, . CH : CH . CO . GB.{GB.,\ + H^O. 

 CeHs . CH : CH . CO . CH(CH,>.+CeH5CH0 = CeH, . CH . CH, . CO . C(CH,), 



CH.CeH, 



CH.C^H, 

 CH, . CH . CH, . CO . C{GE.^)^ + C.H5CHO = C.H, . CH . C . CO . C(CH,)a 



CHCeH CH . CH 



JU-J. 



We also found that the commercial monomethyl-acetylacetone, which 



