Insights on the mechanism for synthesis of methylenedianiline from
aniline and formaldehyde through HPLC–MS and isotope tracer
studies
a
a
a
a
Chen Ye Wang a,b, Hui Quan Li a, , Li Guo Wang , Yan Cao , Hai Tao Liu , Yi Zhang
*
a Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China
b Graduate School of Chinese Academy of Sciences, Beijing 100049, China
Received 29 May 2012
Available online 24 October 2012
Abstract
The mechanism for synthesis of 4,4-methylenedianiline (MDA) via condensation reaction of aniline with formaldehyde has
been studied extensively in this paper. The intermediate and by-products were isolated and identified. The combination of isotope
labeling and HPLC–MS characterizations disclosed that the reaction proceeded through an SN2 reaction mechanism. Moreover, the
effect of aniline/formaldehyde molar ratio on the formation of MDA was investigated. This work would be of significance to
understand the reaction mechanism deeply and provide valuable information for further improving the yield of desired product.
# 2012 Hui Quan Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: 4,4-Methylenedianiline; Condensation reaction; Mechanism; HPLC–MS; Isotopic tracer
Methylenedianiline (MDA) has been widely used as starting material for the production of 4,4-methylene
diphenylene diisocyanate (MDI), which is an important precursor for the manufacture of polyurethanes. A variety of
methods have been reported for the synthesis of MDA [1–3]. Ongoing efforts were devoted to developing new
catalysts [4–6] or optimizing reaction conditions [7,8]. Industrially, MDA is obtained from the reaction of aniline with
formaldehyde in the presence of liquid acid catalysts. Nevertheless, few reports have dealt with the research on the
formation process of the intermediate and by-products. Therefore, it is necessary to use appropriate characterization
methods, thus giving insights on the mechanism for the MDA synthesis.
In this work, MDA was synthesized by the condensation reaction of aniline and formaldehyde in the presence of
HCl. The intermediate and major by-products were isolated and characterized, and DCl was used as a probe to study
the deuterium distribution in products. Using high performance liquid chromatography–electrospray tandem mass
spectrometry (HPLC–MS) analysis, the structures of products can be confirmed, and the related mechanism of MDA
synthesis from aniline and formaldehyde via multistep reactions is discussed. Additionally, the effect of aniline/
formaldehyde molar ratio on the formation MDA was also studied.
It should be mentioned that Kishore [9] proposed the condensation process consisting of a series of rearrangement
reactions in previous literature as shown in Scheme 1. Firstly, aniline first reacts with formaldehyde to provide
* Corresponding author.
1001-8417/$ – see front matter # 2012 Hui Quan Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.