Thermodynamic Aspects of Thermal Decomposition and Charge-Transfer-Induced Chemiluminescent Decomposition for Bicyclic Dioxetanes Bearing a 4-(Benzothiazol-2-yl)-3-hydroxyphenyl Moiety

Uncatalyzed thermal decomposition (TD) and charge-transfer-induced decomposition (CTID) of dioxetanes were investigated to determine their thermodynamic characteristics. The dioxetanes examined were a series of 1-[4-(benzothiazol-2-yl)-3-hydroxyphenyl]-4,4-dimethyl-2,6,7-trioxabicyclo[3.2.0]heptanes, 1a−d, bearing an alkyl substituent R, e.g., methyl, ethyl, isopropyl, or tert-butyl, at the 5-position and a parent dioxetane 1e with R = H. X-ray single crystallographic analysis was achieved for 1a−d. Both free energies of activation, ΔG⧧TD and ΔG⧧CTID, increased in the order 1a ≤ 1b < 1c < 1d. The free energy difference ΔΔG⧧ = ΔG⧧TD − ΔG⧧CTID was ca. 27 kJ mol−1 regardless of the substituent R. However, the use of Taft’s dual-substituent parameter suggested that CTID was more sensitive to the polarity of the substituent R than TD. The entropy term for CTID, ΔS⧧CTID, decreased from zero to a large negative value in the order of tert-butyl, isopropyl, ethyl, and methyl, whereas ΔS⧧TD did not show a similar tendency.

本研究对无催化热分解（TD）和电荷转移诱导分解（CTID）的叠氮化物进行了探究，以确定其热力学特性。所研究的叠氮化物为一系列1-[4-(苯并噻唑-2-基)-3-羟基苯基]-4,4-二甲基-2,6,7-三氧杂双环[3.2.0]庚烷，1a−d，在5位上带有烷基取代基R，例如甲基、乙基、异丙基或叔丁基，以及亲本叠氮化物1e，其中R = H。对1a−d进行了X射线单晶分析。活化自由能ΔG⧧TD和ΔG⧧CTID均按1a ≤ 1b < 1c < 1d的顺序增加。无论取代基R如何，自由能差ΔΔG⧧ = ΔG⧧TD − ΔG⧧CTID约为27 kJ mol−1。然而，使用泰夫特的双重取代基参数表明，CTID对取代基R的极性比TD更为敏感。对于CTID的熵项ΔS⧧CTID，其值从零降至较大的负值，顺序为叔丁基、异丙基、乙基和甲基，而ΔS⧧TD则未显示出类似的趋势。