1H NMR analysis of the tolylene-2,4-diisocyanate-methanol reaction

Article abstract of DOI:10.1016/j.cclet.2010.02.017

Tolylene-2,4-diisocyanate (2,4-TDI) 1 reacts with methanol through two simultaneous paths in the polyurethane reaction, which involve two different intermediates - tolylene-4-carbamatic-2-isocyanate 2 and tolylene-2-carbamatic- 4-isocyanate 3, and the final product is tolylene-2,4-dicarbamate 4. The-CH ₃ chemical shifts in benzene ring in compounds 1, 2, 3 and 4 can be easily tested and well distinguished, through which those four compounds are quantified and their kinetics are investigated. It shows that four rate constants for the tolylene-2,4-diisocyanate-methanol reaction in CCl₄ at 50°C are k₁ = 9.6 × 10^-2 h^-2 mol^-2 min^-1, k₂ = 1.4 × 10^-2 h^-2 mol^-2 min^-1, k₃ = 4.0 × 10^-3 h^-2 mol^-2 min^-1, k₄ = 1.4 × 10^-3 h^-2 mol^-2 min^-1. (k₁ is the reaction rate constant from compounds 1 to 2; k ₂ is the reaction rate constant from compounds 1 to 3; k₃ is the reaction rate constant from compounds 3 to 4; k₄ is the reaction rate constant from compounds 2 to 4).

Full text of DOI:10.1016/j.cclet.2010.02.017

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 853–855
www.elsevier.com/locate/cclet
1H NMR analysis of the tolylene-2,4-diisocyanate–methanol
reaction
c
Peng Fei Yang a, Yong De Han a, Tian Duo Li a,b, , Jun Ying Li
*
a Key Laboratory of Fine Chemicals (Shandong Province), Shandong Institute of Light Industry, Jinan 250353, China
b Science and Technology Office, Shandong Institute of Light Industry, Jinan 250353, China
c School of Chemical Engineering, Shandong Institute of Light Industry, Jinan 250353, China
Received 3 November 2009
Abstract
Tolylene-2,4-diisocyanate (2,4-TDI) 1 reacts with methanol through two simultaneous paths in the polyurethane reaction, which
involve two different intermediates – tolylene-4-carbamatic-2-isocyanate 2 and tolylene-2-carbamatic-4-isocyanate 3, and the final
product is tolylene-2,4-dicarbamate 4. The –CH3 chemical shifts in benzene ring in compounds 1, 2, 3 and 4 can be easily tested and
well distinguished, through which those four compounds are quantified and their kinetics are investigated. It shows that four rate
constants for the tolylene-2,4-diisocyanate–methanol reaction in CCl4 at 50 8C are k1 = 9.6 ꢀ 10ꢁ2 hꢁ2 molꢁ2 minꢁ1
,
k2 = 1.4 ꢀ 10ꢁ2 hꢁ2 molꢁ2 minꢁ1, k3 = 4.0 ꢀ 10ꢁ3 hꢁ2 molꢁ2 minꢁ1, k4 = 1.4 ꢀ 10ꢁ3 hꢁ2 molꢁ2 minꢁ1. (k1 is the reaction rate
constant from compounds 1 to 2; k2 is the reaction rate constant from compounds 1 to 3; k3 is the reaction rate constant from
compounds 3 to 4; k4 is the reaction rate constant from compounds 2 to 4).
# 2010 Tian Duo Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Tolylene-2,4-diisocyanate; Polyurethane reaction; Kinetics
The reaction kinetics of tolylene-2,4-diisocyanate (2,4-TDI) and methanol have been reported to be a
parallel and series reaction containing two simultaneous reaction paths instead of one reaction path [1,2]
(Scheme 1). There are a lot of researches about the reaction kinetics [3–5]. However, the distinction between k1
and k3, k2 and k4 could not be easily detected by that way [6] and some assumptions must be done to deduce the
kinetic equation [7,8]. NMR spectroscopy is a good way to solve the problem [9]. For instance, Dubois et al. [10]
investigated the 2,4-TDI–hydroxyl terminated polybutadiene reaction with 13C NMR and found that the variation
of carbamate groups in polyurethane could be well distinguished during the whole reaction process. Yet,
quantitative study seems impossible because the test time is too long to acquire accurate spectra.
In this contribution, 1H NMR (Bruker, AVANCE II 400) is used to analyze the chemical shifts of methyl group in
benzene ring during the 2,4-TDI–methanol reaction. The –CH3 chemical shifts for compounds 1, 2, 3 and 4 in CDCl3
can be well distinguished.
* Corresponding author at: Science and Technology Office, Shandong Institute of Light Industry, Jinan 250353, China.
E-mail address: litianduo@163.com (T.D. Li).
1001-8417/$ – see front matter # 2010 Tian Duo Li. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.02.017

854
P.F. Yang et al. / Chinese Chemical Letters 21 (2010) 853–855
Scheme 1. Two simultaneous paths for the 2,4-TDI–methanol reaction.
1. Results and discussion
First, 2,4-TDI (2.3 mmol, 0.33 mL) and methanol (4.6 mmol, 0.19 mL) are mixed in CCl4 (73 mmol, 7 mL) and
reacted at 50 8C. FT-IR (Mettler Toledo, React IR IC10) in situ is used to monitor the reaction process [11]. The
relationship between total amount of –NCO and time (t) can be obtained accurately and the rate constants can be
calculated out. As a result, the rate constant in the initial stage is kinitial = 1.1 ꢀ 10ꢁ1 hꢁ2 molꢁ2 minꢁ1 (0 ꢂ j ꢂ 19%)
and that in the final stage is kfinal = 5.4 ꢀ 10ꢁ3 hꢁ2ꢃmolꢁ2ꢃminꢁ1 (62% ꢂ j ꢂ 70%). The extent of reaction (j) can be
calculated from the extent of total –NCO consumption.
Second, the same reaction is carried on again. When the reaction reaches certain moments (t), part of the reaction
mixture (0.5 mL) is taken out at corresponding intervals to test 1H NMR spectra. Thus, a series of 1H NMR spectra is
obtained with different extents of the reaction. According to the references [12], the chemical shifts for –CH3 in
benzene ring in compounds 1, 2, 3 and 4 can be attributed to 2.30, 2.27, 2.21 and 2.19 ppm, respectively. Thus, the
amounts of compounds 1, 2, 3 and 4 are determined accurately (Fig. 1).
1
The extent of reaction (j) can also be calculated out from H NMR spectra
I2 þ I3 þ 2I4
j ¼
(1)
2ðI1 þ I2 þ I3 þ I4Þ
where I1, I2, I3 and I4 are the integrations of peak areas for compounds 1, 2, 3 and 4, and they can represent the amounts
of these four compounds. The mol percentages of compounds 1, 2, 3 and 4 to j in the 2,4-TDI–methanol reaction are
shown in Fig. 2.
The amount of compound 1 decreases and the amount of compound 4 increases continuously. But, in sharp contrast,
there is a maximum mol percentage of compounds 2 (j = 60%) and 3 (j = 40%), which are 74% and 12%, respectively.
Fig. 1. 1H NMR spectra of 2,4-TDI–methanol reaction for 1.5 h.

P.F. Yang et al. / Chinese Chemical Letters 21 (2010) 853–855
855
Fig. 2. The variation of 1, 2, 3 and 4 mol percentage to j.
Moreover, there is no compound 4 in the reaction system when j is lower than 19%. Only k1 and k2 take effect, so the
relationship between k1 and k2 in the parallel reaction can be calculated:
I2;j¼19% ꢁ I2;j¼0
k1 DI2
¼
¼
¼ 6:6
k2 DI3 I3;j¼19% ꢁ I3;j¼0
Likewise, there is no compound 1 in the reaction system when j is higher than 62% and lower than 70%. Only k3
and k4 take effect, so the relationship between k3 and k4 in the parallel reaction can be calculated:
I2;j¼70% ꢁ I2;j¼62%
k3 DI2
¼
¼
¼ 3
k4 DI3 I3;j¼70% ꢁ I3;j¼62%
Finally, considering the relationship of kinitial = k1 + k2 and kfinal = k3 + k4, the four rate constants for the 2,4-TDI–
methanol reaction in CCl4 at 50 8C can be calculated: k1 = 9.6 ꢀ 10ꢁ2 hꢁ2 molꢁ2 minꢁ1
;
k2 = 1.4 ꢀ 10ꢁ2 hꢁ2 molꢁ2 minꢁ1; k3 = 4.0 ꢀ 10ꢁ3 hꢁ2 molꢁ2 minꢁ1; k4 = 1.4 ꢀ 10ꢁ3 hꢁ2 molꢁ2 minꢁ1
.
Acknowledgments
The authors are grateful to the financial support from the National Natural Science Foundation of China (No.
20676074) and the National Natural Science Foundation of Shandong Province (No. Y2004B04).
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