Kinetics, isotope effects, and mechanism of the reaction of 1,1,1-trifluoro-2,2-bis-(4-nitrophenyl)ethane with piperidine and pyrrolidine bases in dipolar aprotic solvents

Abstract

The kinetics of the reaction of 1,1,1 -trifluoro-2,2-bis-(4-nitropheny1)ethane with piperidine and pyrrolidine bases in a series of solvents [acetonitrile (MeCN), benzonitrile (PhCN), and dimethyl sulphoxide (Me,SO)] are reported. The reaction is complex, leading to a 1 -amino-1 -fluoro-2,2-bis-(4-nitropheny1)ethene as the final product via the intermediate 1,l -difluoro-2,2-bis-(4-nitropheny1)ethene. The reaction is promoted only by primary and secondary amines; tertiary amines appear to be inactive even under reflux conditions. The entropies of activation (ASX/J mol-' K-l) are negative and large ( -183.7 and -162.3) for the reaction with piperidine in PhCN and MeCN; for reaction in Me,SO the value is only -77.4. The kinetic isotope effects (k,/k,) fall between 1 .O and 1.6 at 30 "C. The results obtained are discussed in terms of a multistep mechanism, (€1 C B ) , ~, consisting of a pre-equilibrium followed by fast addition-elimination steps.

Kinetics, isotope effects, and mechanism of the reaction of 1-nitro-1(4-nitrophenyl)alkanes with DBU in acetonitrile

“…Their values depend on the amount of impurities present in the system, but despite this we estimated the dissociation constant Kd of the ion-pair product of MNNPP-., DBUH' to be larger than 1 x and 3. 3 x what is in good agreement with the value of 1.96 x obtained by spectrophotometric method using equation (4).…”

“…If the product is an ion pair, a plot of cAH/OD uersus l/cB will be a straight line of intercept 1 / ~; and slope ~/K,E. A similar treatment for ion products leads to equation (4) (4) where…”

“…M.p. 4 2-Methyl-l-phenylpropan-1 -01.-This was obtained by reduction of isobutyrophenone (0.3 mol) with NaBH, (1.35 mol) in 75% methanol (1 dm3). After the addition of isobutyrophenone the reaction mixture was heated under reflux for 15 min, and then dilute HCl (1 : 1; 200 cm3) was added.…”

“…1,8-Diazabicyclo[5. 4.O]undec-7-ene (DBU).-The commercial product purchased from Aldrich was dried over potassium hydroxide pellets and then fractionally distilled under reduced pressure. The middle fraction was collected and used.…”

Kinetics, deuterium isotope effect and mechanism of the reaction of 1,1,1-trifluoro-2,2-bis(4-nitrophenyl)ethane with 1,1,3,3-tetramethylguanidine in aprotic solvents

“…Ar,CHCF, + B -% Ar,C=CF2 A Ar,C==CFB (1) In the case of the reaction of Ar2CHCF3 promoted by TMG derivatives [R-N=C(NMe2)2 (R = Me or Ph)] and amidines [R-N=CMe(NMe,)] difluoroalkene Ar,C=CF, was isolated as a final product. An attempt to detect the difluoroalkene in our reaction mixture was not successful.…”