Phenol in Mixed Acid Benzene Nitration Systems

Abstract

Phenol was detected for the first time in the mononitrobenzene production process by benzene adiabatic nitration, supporting the theory that proposes phenol as the precursor of nitrophenols, unwanted byproducts. For that, analytical procedures (based in liquid and gas chromatographic techniques) have been developed and improved that aim to detect these chemical species both in the industrial nitration process as well as in laboratory tests at different reaction conditions. The obtained results confirmed the proposed and accepted mechanism for the nitrophenols formation during benzene nitration, showing that phenol is indeed the nitrophenolic byproducts precursor. Moreover, it is shown the phenol's high reactivity even at smooth reaction conditions (namely low temperature and low sulfuric acid concentration), which explains the difficulty of detecting this compound within the reaction medium using the analytical techniques applied for monitoring benzene nitration process. In this study, it was also discovered that 4-mononitrophenol had higher affinity into the aqueous acid phase when compared to the other nitrophenolic byproducts (2-mononitrophenol; 2,4-dinitrophenol; 2,6-dinitrophenol; and 2,4,6-trinitrophenol) that have more affinity into the organic phase. Phenol distribution between both reaction phases was found to be similar to the majority of the nitrophenols, i.e., it is present in higher concentration in the organic phase.

Safe, Green, and Efficient Synthesis of m‐Dinitrobenzene via Two‐Step Nitration in a Continuous‐Flow Microreactor

“…Since the reaction conditions could be precisely controlled and the occurrence of side reactions was reduced, the yield of dinitrobenzene was more than 99.0 % and the selectivity of m‐DNB was 90.88 %. During the nitration reactions, the formation of self‐reactive nitrophenols is difficult to avoid [19] . 2,4,6‐trinitroresorcinol, a major by‐product in the dinitrobenzene production process, is self‐reactive substance and has led to tragic explosion incidents in China [20] .…”

“…During the nitration reactions, the formation of self-reactive nitrophenols is difficult to avoid. [19] 2,4,6-trinitroresorcinol, a major by-product in the dinitrobenzene production process, is selfreactive substance and has led to tragic explosion incidents in China. [20] Notably, the amount of nitrophenol is very small and must be concentrated 50 times before it can be detected.…”

Thermal Risk Assessment of the Complex Nitration Process through Safety Operating Space Analysis and Optimization

“…Wang investigated 854 chemical accidents with casualties in China from 2015 to 2019 and found that the nitration accidents caused the most casualties due to the explosion and fire within the hazardous reaction processes. Researchers have undertaken extensive efforts to ensure the safety of nitration production. − …”

Thermal Behavior and Decomposition Pathway for Nitrophenols and Sodium Nitrophenolates

“…2−6 The oxidation of benzene by nitric acid forms the side-product phenol, which acts as the precursor for nitrophenols under nitration conditions. 7 These nitrophenols will be transformed to the corresponding sodium nitrophenolates after washing the MNB with alkaline solution. Nitrophenols and sodium nitrophenolates as side products are intractable in terms of environment, safety, and processing cost.…”

“…Mononitrobenzene (MNB) is an important organic intermediate in the fine chemical industry and has been widely used for manufacturing dyes, pesticides, and explosives . MNB is synthesized through nitration of benzene, in which the main side products formed are nitrophenols (the reaction route of nitrophenolic side products is shown in Figure ), such as mononitrophenols, dinitrophenols, and dinitrobenzene. − The oxidation of benzene by nitric acid forms the side-product phenol, which acts as the precursor for nitrophenols under nitration conditions . These nitrophenols will be transformed to the corresponding sodium nitrophenolates after washing the MNB with alkaline solution.…”