Influence of Substituents on Reactivity and Reaction Mechanism of SN Reaction of Some Organophosphorus Compounds; Relied on Linear Free Energy Relationship

APCBEE Procedia Pub Date : 2014-01-01 DOI:10.1016/j.apcbee.2014.01.008

Bilkis Jahan Lumbiny , Zhang Hui , M. Azizul Islam

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Abstract

The tetracoordinated organophosphorous compound (4 - Chlorophenyl 4 - methyl phenyl Chlorophosphate, 1) were synthesized, characterized and nucleophilic substitution reaction (pyridinolysis) were investigated in acetonitrile at 5.0^oC by varying substituents in nucleophiles. The reactivity is expressed in terms of second-order rate constant, k2 and measured conductometrically. Physical organic chemistry tools mainly Hammett (ρ), Brönsted (β) Linear Free Energy Relationship (LFER) coefficients being determined in quest for the mechanistic information by comparing pyridinolysis of structurally similar organophosphorous compounds reported earlier. Nice linear correlation being found for Hammett (logk₂ vs σx) and Brönsted (logk₂ vs pK_a(x)) plots. In the light of the reported results the LFER obtained for 1 with negative value of the ρ_X, −5.78 and large positive value for β_X, 1.17 can be interpreted as S_N2 process, with greater extent of bond formation in TS of 1.

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取代基对某些有机磷化合物SN反应活性及反应机理的影响依赖于线性自由能关系

合成了四配位有机磷化合物(4 -氯苯基4 -甲基苯基氯磷酸，1)，对其进行了表征，并在5.0℃的乙腈中通过亲核试剂中不同取代基进行了亲核取代反应(吡啶分解)。反应性用二阶速率常数k2表示，并用电导法测量。物理有机化学工具主要是Hammett (ρ)， Brönsted (β)线性自由能关系(LFER)系数的测定，通过比较前人报道的结构相似的有机磷化合物吡啶分解的机理信息。在Hammett (logk2 vs σx)和Brönsted (logk2 vs pKa(x))图中发现了很好的线性相关性。从已有的结果来看，1的ρX为负值，−5.78，βX为较大的正值，1.17的LFER可以解释为SN2过程，在1的TS中形成键的程度更大。

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APCBEE Procedia

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