Indian Journal of ChemistryVol. 19A, June 1980, pp. 523-526

Reaction Between Maleic Anhydride & Substituted Amines In

Solid State

R. P. RASTOGI, N. B. SINGH· & A. K. SRIVASTAVAtDepartment of Chemistry. University of Gorakhpur, Gorakhpur

Received 12 September 1979; accepted 6 November 1979

The reactions in the solid state between maleic anhydride and p-chloroaniline, p-bromoaniline, p-anisidineand m-nitroaniline have been studied. Analytical data and IR spectra show that the products are corresponding malea-mic acids. The thickness of the product layer (~) is found to depend on log of reaction time ( t) when solid-solid reac-tion is studied. The solid-gas reaction has also been studied and the square of change In weight is found to be propor-tional to time. The mechanism of solid-solid as well as solid-gas reaction has been discussed. Some comments onlattice rearrangement and energy changes during the reaction have also been made.

REACTIONS between maleic anhydride andamines in eutectic melts have been studiedrecently', Mixtures of amines and benzo-

phenone provided an eutectic melt in which benzo-phenone was an inert component. In these reactionsmaleamic acids, characterised by neutralisation equi-valents and IR spectra, were obtained in good yields(65-95%) within a few minutes. In order to havea comprehensive picture of the chemistry of maleamicacids, we report here the results of solid state reac-tions of maleic anhydride with p-chloroaniline, p-anisidine, p-bromoaniline and m-nitroaniline. Thisis a typical organic solid state reaction of the typeA(s) + B(s) - C(s) in which a new covalent bondis formed, although quite a few coordinate bondformation reactions in the solid state have beenstudied earlier+", Reactions when C is an additioncompound, are more common.

Materials and MethodsMaleic anhydride (S. Merck), p-chloroaniline

(BDH) and p-anisidine (BDH) were purified byrepeated distillation under reduced pressure. p-Bromoaniline (BDH) and m-nitroaniline (Riedel)were purified by fractional crystallization from ethylalcohol-water.

Solid state reactions did not proceed to comple-tion since the reaction products did not have sharpmelting points. It was difficult to isolate the malea-mic acids from the corresponding solid mixture.To prove that the maleamic acids obtained by solidstate reaction were the same as those obtained fromthe reaction of maleic anhydride and correspondingamines (1 :1) in acetone and separated by fractionalcrystallisation, the following experiments were con-ducted. The amine and maleic anhydride weremixed in 1: 1 molar ratio and grounded in a glassmortar. The unreacted maleic anhydride was re-moved from the reaction mixture by dissolving it

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in water. The residue, which might contain un-reacted amine and the maleamic acid was subjectedto paper chromatography using n-butanol-aceticacid-water (60:15:25, v/v) as solvent system andninhydrin solution (3 mg ninhydrin in 100 ml ace-tone) as locating reagent. The Rr values of malea-mic acids were compared with those obtained usingrecrystallised maleamic acids. These were foundto be identical. Further confirmation was providedby comparing the IR spectra of solid mixture andthat of the reaction product obtained from acetone.These were found to be identical.

Infrared spectra of maleic anhydride, p-anisidine,p-bromoaniline, p-chloroaniline, m-nitroaniline andthe corresponding maleamic acids crystallized fromacetone were recorded in KBr phase on a Perkin-Elmer 521 spectrophotometer. IR spectra of themaleamic acids obtained by solid state reactionswere also recorded.

Kinetics of solid state reaction - The solid statereaction of maleic anhydride with p-chloroaniline,p-anisidine and p-bromoaniline, was studied bycapillary techniques. A glass capillary sealed at oneend was half-filled with the amine and the surfacewas made smooth by a glass rod. The other halfof the capillary was filled with maleic anhydride.The capillaries were kept in an air thermostat main-tained at a constant temperature. The kinetics ofthe reaction which was initiated by a change incolour at the junction of the two reactants, wasfollowed by measuring the thickness of the reactionproduct formed at different intervals of time. Theexperiments were performed at different temperaturesand for particles of different sizes. Such a study couldnot be made in the case of m-nitroaniline since adiffuse product layer was formed in this case.

Kinetics of solid-gas reaction - The method usedfor this study was the same as described previously+A known amount of maleic anhydride was taken ina tube fitted with a Bl9 male joint. The amine ofknown weight was taken in another tube fitted with

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INDIAN J. CHEM., VOL. 19A, JUNE 1980

a B19 female joint. The tubes were joined andplaced horizontaIly in a thermostat. The kineticsof the reaction was followed by noting the changein weight of the tube containing the amines at diffe-rent intervals of time. The kinetics was foIlowedat different temperatures.

Results and DiscussionIR spectra (Vmax in cm-I) of the solid-state reaction

products purified by crystallization from acetone,exhibit bands for \leOOH and VeONH2"'" 1700 and1630 respectively (Table 1). This coupled with theresults on elemental analyses (Table 1) show that theproduct of the reaction is maleamic acid. FromTLC studies it follows that only one product isformed.

The IR spectra of both p~anisoylmaleamic acidcrystallized from acetone and the reaction productobtained by solid state reaction between maleicanhydride and p~anisidine are identical in theregions where carboxylic and -CONH groupsnormally appear, indicating that the two productsare the same. Paper chromatographic studies alsoprove that the solid state reaction products areidentical (similar Rr's) with those obtained fromacetone.

The kinetic data for the solid state reactions arefound to fit, except for t = 0, the equation

e: = Clog t + k .. (1)

where e: is the thickness of the product layer andt denotes time. Further C and k are constants.It is obvious that e: is indeterminate when t = 0or t = 00 The above equation has been deducedby rigorous arguments assuming the propagationof reaction through channels and capillaries andtheir subsequent blocking. This picture seemsplausible since the propagation of the reaction mustinvolve formation of cracks in the solid matrixfollowed by formation of channels through whichreactant can diffuse. The process would be repeatedover and over again. In this way, solid state re-action can proceed easily without involving bulkdiffusion through organic solid which is not otherwisefeasible. The plots of e: versus t are linear for thereaction of maleic anhydride with p~chloroanilinep~bromoaniline and p-anisidine at different tem-peratures. A typical plot is shown in Fig. 1. The

0·20

0·16

, 0·12

""0·08

O.O°Q.'';;O--'----;O;':;.4~~~Q.;:-';8:--~---71.2::---'-----:I.':-6-~-:2:-'::.O'--loqt_

Fig. 1 - Kinetic data for reaction between maleic anhydrideand p~hloroaniline at different temperatures.

524

parameters of Eq. (1) at different temperatures andfor particles of different sizes, given in Tables 2 and 3,show that C is independent of temperature andparticle size while the intercept k increases withincrease in temperature. Since the solid-solidreactions are diffusion-controlled, k ought to be afunction of the diffusion coefficient of diffusingspecies. However, the exact relationship should beknown before any inference from the temperaturedependence of k can be drawn.

Plots of log k against liT are linear (Fig. 2) indi-cating that Arrhenius type equation is obeyed. Fromthe slope of the curves, the energies of activationhave been computed and are given in Table 2. Thevalues of energy of activation suggest that mostprobably diffusion occurs by surface migration.

The effect of particle size on the rate constants areshown in Fig. 3 and the parameters calculated fromthe linear plots are given in Table 3.

The kinetic data for the solid-gas reaction arefound to fit the equation

W2 = kifwhere W is change in wight at any time

.. (2)

t and ke

-1·30

-1.40...:.....e -\.50

--/.70 L- -'- --'__ ~..::......o.-3.10 3.403.2.0 3.30

t )(.103

Fig. 2 - Effect of temperature on k for the reaction of p-chloroaniline (0), p-bromoaniline (e) and p-anisidine «()

with maleic anhydride.

0·08

0·06

, 0-04"'lI!

o-oa

0~~8--~~~'0--~Z~.2--~~~'4----

l09r-

Fig. 3 -"Effect of particle size on k for the reaction of p-chloroaniline «», p-bromoaniline (e) and p-anisidine (. )

with maleic anhydride.

RASTOGI et al. : REACTIONS BETWEEN MALEIC ANHYDRIDE & AMINES

Maleamie acid

N-(p-Chlorophenyl)

N-(p- Bromopheny I)

N-(m-Nitrophenyl)

N-(p-Anisoyl)

TABLE 1- CHARACTERISATIONDATA OF THE MALEAMIC ACIDS·

m.p. Found (%) (calc.) IR Vm.x (crrr ')°C

C H vNH vCOOH vCONH

204.4 52.61 3.53 3195 1706 1634(53.21) (3.54)

190.5 45.33 2.88 3260 1690 1622(44.43) (2.96)

195.5 50.98 3.64 3185 1709 1626(50.81) (3.38)

185.6 59.20 5.01 3244 J 1684 1612-1616(59.67) (4.56) 3232 1696

• Acids were erystallised from acetone.

TABLE 2 - KINETIC PARAMETERSOF EQ. (1)[Particle size = 150-170 mesh]

Temp.(±I°C)

25303540

25303540

25303540

k(em)

C(cm/hr)

Eo(kcal/mol)

p-CHLOROANILINE

TABLE 4 - PARAMETERSOF EQ. (2)

[particle size = 150-170 mesh]

Temp. k, x 10'(±I°C) (g/hr)

p-ANISIDINE

20 0.5825 0.8030 1.4335 2.00

p-CHLOROANILINE

20 0.6025 0.9030 1.3335 1.82

m-NITROANIUNE

20 0.5730 1.2534 1.7640 2.50

p-BROMOANILINE

20 . 1.0834 1.4840 3.3343 4.44

0.0200.D280.0370.44

0.0100.0110.0120.010

7.6

p-BROMOANILINE

0.0200.0240.0320.D35

0.300.0370.0440.050

0.010.010.010.01

4.9

p-ANISIDINE

0.040.040.040.04

6.5

TABLE 3 - PARAMETEROF EQ. (1) FOR PARTICLES OF DIFFERENTSIZES

[Temperature = 25 ± 1°C]

Particle size k C(mesh) (em) (cm/hr)

p-CHLOROANILINE

100-120 0.052 0.013120-150 0.038 0.015150-170 0.020 0.010170-200 0.018 0.012

p-BROMOANILINE

100-120 0.040 0.01120-150 0.032 0.01150-170 0.020 0.01170-200 0.016 0.01

p-ANISIDINE

100-120 0.061 0.04120-150 0.046 0.04150-170 0.036 0.04170-200 0.025 0.04

E.(kcal/mol)

15.2

13.0

13.8

20.5

is the rate constant. The values of k, for the reactionsare recorded in Table 4. Energy of activation forthese reactions has also been estimated and the valuesare given in Table 4.

The values of energy of activation for the reactionswith p-anisidine, p-chloroaniline and m-nitroanilineare almost the same, and less than the heat ofsublimation of maleic anhydride which is (18.4kcal/mol). However, for the reaction with p-bromo-aniline, the energy of activation is greater than theheat of sublimation of maleic anhydride. This suggeststhat the reactions do not take place exclusively viathe vapours in all the cases except the reaction withp-bromoaniline. Probably surface migration alongthe glass surface also takes place. It should benoted that energy of activation of the gas reaction ismuch greater than that for the case when the re-

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INDIAN J. CHEM., VOL. 19A, JUNE 1980

Fig. 4 - Molecular packing at plane Z-1/4 looking down(001) plane in N-(p-chloropheny\ ) rnalearnic acid.

actions are kept adjacent to each other. This is sosince in the latter case surface migration predomi-nantly occurs which provides much easier path.

Some comments are called for on the latticerearrangement during solid state reaction and asso-ciated energy changes.

Lattice-rearrangement and energy changes - Re-cently Prasad and Mandal" investigated the crystalstructure of p-chlorophenylmaleamic acid preparedby us and found that the crystal lattice belongs tothe monoclinic system with the following cell cons-tants : a = 12.68 A, b = 11.69 A, c = 7.35 A,~= 115.5°, space group = Pila, Z = 4, deae=1.545g cm ? and dobs = 1.54 g/cm-3• They foundthat the molecules within the unit cell are arrangedin two layers parallel to (001)plane and they arenearly planar and the bond lengths and the bondangles are normal (Fig. 4). If UA', UB and Up arethe cell volume of maleic anhydride (431 A 3),p-chlorophenyleneamine (595.5 A3) and the malea-mic acid (1089.5 AS) respectively, UP-(UA+UB)/

526

(UA+UB) would be a measure of fractional changeof cell volume when the guest molecule enters thehost molecule. The magnitude of fractional changecomes out to be 6.15%. This suggests that entropychanges during the reaction are quite small.

In the set of reactions considered above, we canestimate the heat of reaction from a knowledge ofbond energies. Heat absorbed during the ruptureof N-H and C-O bonds is 177.4 kcal/molwhereas heat evolved during the formation of N-Cand O-H bonds is 180.3 kcal/mol. Thus in thereaction the energy expenditure is quite small, sinceheat of reaction, L:,H would be just 2.9 kcal/mol.Negative sign is expected since for solid state reactionL:,S:::;O and for the reaction to occur t:,.G has tobe negative. Preliminary thermochemical experi-ments confirm that the reaction is exothermic andthat the heat of reaction is of the order of 4 kca1jmol.

AcknowledgementThe authors are grateful to the Director, Central

Drug Research Institute, Lucknow for providingnecessary facilities for microanalyses and infraredspectra.

References1. SINGH, H. & RASTOGI, S., Indian J. Chern•• 148 (1976),

809.2. ARROWSMITH,R. J. & SMITH,J. M., Ind. Engng Chem.,

Fundamentals, 5 (1966), 327.3. GLUZMANN, M. Kh. & MILNER, R. S. Tr. Khim. Fak. i.

Nauch.Inst. Khim •• 17 (1961), 17.4. RASTOGI,R. P., BASSI,P. S. & CHADDHA,S. L. J. phys,

Chern•• 67 (1963), 2569.5. PRASAD. S. M. & MANDAL, D. K., Indian J. Phys •• 52A

(1978), 585.