Uç asetilenlerin kenetlenmesinde sübstitüent etkisinin incelenmesi

Abstract

ÖZET Terminal asetilenler, buzlu asetik asitte bakır (I) tuzlarının katalitik etkisiyle enin'lere dimerleşmektedirler. CU2O 2ROCH >ROC-CH=CHR CH3COOH Bu çalışmada, p-nitrofenilasetilen (pNFA), mesitilasetilen (MA) ve fenilasetilen (FA) sentezlenerek, dimerleşme tepkimesinde aromatik halkadaki sübstitüentlerin etkisi araştırıldı. Ayrıca bu asetilenlerin dimerleşme hızları saptandı. Her üç asetilen, CU2O katalizör eşliğinde kolaylıkla polimerik bakır (I) asetilidlerini oluşturmaktadırlar. pNFA ve MA'nın reaksiyonu bu basamakta kalırken, FA beklenen enin ürünlerini vermektedir. Ayrıca çapraz Straus deneyleri sonucunda sadece FA-MA'nın ürünleri gözlenmektedir. FA-pNFA ve MA-pNFA çapraz-kenetlenme ürünleri oluşmamaktadır. Çapraz kenetlenme deneylerinde aşağıdaki denge tepkimesinin oluştuğu saptanmıştır. PhC=CH + PhC*=C-Cu F^ PhC*=CH + PhC=C-Cu Mesitilasetilenin aktif olmayışı, o-metil gruplarının sterik etkisine yorumlanırken, pNFA'nın beklenilmeyen olumsuz tepkisi, diğer bu bileşiğin asetilid anyonunun artan polaritesine bağlanabilir.

SUMMARY Terminal acetylenes dimerize to enynes under the catalytic effect of Cu (I) salts in glacial acetic acid. C112O 2RChCH >RCsC-CH=CHR CH3COOH In the present work, p-Nitrophenylacetylene (pNFA), mesitilacetylene (MA) and phenylacetylene (FA) have been synthesized and the effects of the substituents on the aromatic ring in the dimerization reaction have been studied. The determination of the relative rates of dimerizations was aimed. Polymeric copper (I) acetylides are formed easily in the presence of CU2O catalyst by all three acetylenes. While pNFA and MA remain unchanged at this stage, phenylacetylene gives the expected enyne. Cross-coupling Straus experiments result only, in the formation of FA-MA products. FA-pNFA MA-pNFA cross-coupling products are not formed. In the cross-coupling experiments the existence of the following equilibrium reaction is detected. PhOCH + Ph*CfeC-Cu F=* Ph*C=CH + PhC=C-Cu While the unactivity of MA was attributed to the steric effect of the 0- methyl groups, the surprising inertness of pNFA could be due to the increased polarity of the corresponding acetylide anion of this compound.in SUMMARY Terminal acetylenes dimerize to enynes under the catalytic effect of Cu (I) salts in glacial acetic acid. Cu20 2RC=CH >ROC-CH=CHR CH3COOH İh the present work, p-Nitrophenylacetylene (pNFA), mesitilacetylene (MA) and phenylacetylene (FA) have been synthesized and the effects of the substituents on the aromatic ring in the dimerization reaction have been studied. The determination of the relative rates of dimerizations was aimed. Polymeric copper (I) acetylides are formed easily in the presence of CU2O catalyst by all three acetylenes. While pNFA and MA remain unchanged at this stage, phenylacetylene gives the expected enyne. Cross-coupling Straus experiments result only, in the formation of FA-MA products. FA-pNFA MA-pNFA cross-coupling products are not formed. In the cross-coupling experiments the existence of the following equilibrium reaction is detected. PhOCH + Ph*C=C-Cu F=^ Ph*C=CH + PhC=C-Cu While the unactivity of MA was attributed to the steric effect of the 0- methyl groups, the surprising inertness of pNFA could be due to the increased polarity of the corresponding acetylide anion of this compound.