A Theoretical Study of Reaction of Nitrile Oxides with Ammonia "C
/, ,1111, j j~~I'hM _Hfl Indian Journal of Chemistry Vol. 26A, November 1987, pp. 906-913 A Theoretical Study of Reaction of Nitrile Oxides with Ammonia KRISHAN K SHARMN & ANIL K AGGARWAL Department of Chemistry, Zakir Husain College, University of Delhi, Ajmeri Gate, Delhi 110006 Received 3 February 1987; revised 10 March 1987; accepted 16 Apri/1987 The potential energy hypersurface for the reaction of nitrile oxides, RCNO (R=H, fulminic acid; and R=CH3, acetonitrile oxide) with NH3 as a nucleophile to give oximes RNHzC = NOH has been studied by the MNDO method. The calculations have been performed with complete geometry optimisation using Davidon-Fletcher• Powell method. The bond distance C3 - Nz (denoted by R), between the carbon of nitrile oxide and nitrogen of ammonia, has been employed as the reaction coordinate. The energy along the reaction coordinate is minimised at each point by varying all the parameters (bond lengths, bond angles and the twist angles). The reaction is predict• ed to be exothermic and proceeds in two steps. The first step is the formation of zwitterionic structure as interme• diate via a transition state at R = 1.88 A. This step is the rate-determining step and requires the calculated activa• tion energy of 28.86 kcal mol- I in the case of fulminic acid and 33.10 kcal mol- I for acetonitrile oxide. The sec• ond step which involves transfer of a proton occurs very fast and requires a passage over a further barrier with an activation energy of only 1.96 and 2.17 local mol-t respectively for fulminic acid and acetonitrile oxide. This then leads to the formation of the product amidoxime of Z-configuration, as has been observed experimentally. Recently, we have reported MNDO study on the In the present work, we have carried out a the• reaction of methanol with nitrile oxide (RCNO)l. oretical study of the reactions of ammonia with The reaction involving nitrogen nucleophiles e.g. fulminic acid (HCNO; 1, R = H) and acetonitrile NH3, RNHz, RzNH etc. and nitrile oxides also oxide (CH3CNO; 1, R=CH3) using both as sub• leads to open chain oximes as the products z -7. strates. These reaction systems have been chosen The reaction of RCNO with the nucleophiles ex• as a model to make a comparative study. We were clusively occurs by an attack at carbonz,8. How• particularly interested in the stereochemistry of ever, these reactions also appear to be stereospe• the reaction and in the characteristics of the cific in nature in that only one of the two possible transition state, since the transition state geometry oxime isomers (Z or E) is invariably formed. is not observable experimentally; these can only Nitrile oxide (RCNO) (1), a typical 1,3-dipole, be checked theoretically. reacts with primary and secondary amines stere• ospecificallyz to give only the Z-amidoximes (4 Method of Calculations and5) in which the nucleophile and the - OH The calculations were carried out by the groups are in cis position. With primary amines MNDO method of Dewar and Thiel9• The meth• and ammoniaz the Z-isomer (2) is also thermody• od of Davidon-Fletcher-PowelllO was employed namically favoured but the subsequent isomerisa• for the optimisation of molecular geometries using tion to the more stable E-isomer (3) occurs with MNDO program 11. The transition states were the more bulky secondary amines. found by the usual reaction coordinate method 12, and were confirmed by checking one negative ei• 13. 3 genvalue in the diagonalised Hessian matrix R The second transition state (1'2) was located by (l) "c R transferring the proton from the nucleophile to / -N _ "-... /OH RzN \ /C=N ( the terminal oxygen of substrates at a point when the charge-transfer, from the nucleophile to the OH R~ El substrate, was maximum. The bond distance R, Rz=Mtz or (CHzI41RzNH (Z) C-N R"C ••••N (l) - / 4 NH C3 N2 (denoted by R) was taken as the reaction RNH "- OH RNHz RCNO1 ---! ~HzN / "'-OH coordinate. The heats of formation of the super• 2 molecule (RCNO + NH3) were plotted against the 4 !PhNHIII distance R. In accordance with the predictions of R R Rothman and Lohrl4, the maximum on such a (II 'C-N •• "-...C=N /OH reaction surface is the transition state provided Ph NIII/ - \.OH PhN' (E) the reaction path is continuous. All the results re• 5 ported in this paper were derived without involv- 906 '1'- 'I" jfl!ll" SHARMA & AGGARWAL: THEORETICAL STUDY OF REACTION OF NITRILE OXIDES WITH AMMONIA -6 +6 -6 H- C== N H-C==:N=-=O ,·055 1·160 1·04! ,.,6> ,,,, 0[1'0631 (1-I54J b[I'027J [1-168] (1-199] 'H·0·244 'N = 0·262 reN N R~1 'C ••-0,116 '0" -0,320 hJ3 r~o R,' ..•05 'H,"0'076 , =0'094 H H H N 9 , H ,2 10H~~ : -0.228 \ 1·3/5 4 =-0,226 I I r , ..•'r' Y,f~N , •• 0'f8~ C N N HT007 ", = '1 907 I /, •11, I.JHI H ",i J,,!,i I",,,, • "'Ill ". ,JJ I~"IN, ~ 11j.,; i I I,j, I 'i !J . 'I r r 1.1691.1701.3421.2581.2621.2441.2451.3581.2521.3521.3711.3651.3501.3401.3541.3311.3601.3621.2681.3631.2281.1801.2151.3662.8453.6953.3061.2501.3562.9643.7392.9432.9732.6803.1703.1583.5601.3691.2631.3823.1202.9722.6913.130122.9139.42.6403.151140.72.5872.6742.5822.648146.52.5851.0841.0220.9582.760123.5123.3139.0122.5116.8]49.8120.52.6631.0852.6691.0282.545140.9123.2138.02.622123.4a]60.4].085123.61.307123.1123.92.5641.4872.5701.478136.2138.51.083124.72.728122.6125.0123.71.0201.0781.306124.2120.7139.7121.2122.2145.41.086122.11.0261.0691.068139.91.194125.3123.0122.0137.0II1.048].007rl'Oe121.31.0241.1891.4861.0251.443131.7135.11.471125.1120.9137.71.485122.4122.7138.8137.5124.01.1921.1931.081121.7127.21.067119.3121.8125.51.4931.469128.3115.9118.51.0631.0541.4651.013121.6]80.0123.81.1901.481114.41.089167.0180.0109.2127.41.1881.488].020121.5121.9142.91.4681.1911.015120.61.0]51.19"11.0]61.1861.01613121.4118.6119.21.007115.7118.8121.0114.5114.11.516118.9129.3119.8129.5119.1rRC1.101111.3114.0129.0122.3]20.4120.4122.2120.5121.3130.1]36.8122.9131.7130.4120.7134.6120.0128.9127.3120.1121.7121.5128.7121.01.3211.31562.6567.7163.3749.8462.8061.5949.9161.7360.8049.6949.6849.7361.5873.3361.4651.8561.4151.0261.7161.6861.7271.5973.2973.3573.3452.5959.89 -16.59-8.2444.4928.63 INDIAN180.0 J. CHEM., VOL. 26A, NOVEMBER 1987 q91y Bond length (A) !3.Hf Angles (degree) I) 1.902.00A (kcal mol - 1.387<1.3811.88b1.40d1.47e1.48e2.002.251.451.891.501.871.461.551.901.481.601.801.471.49 < reI' coacoa HNH2C =NOH and H3CNH,C = NOH. Reactants: CH3CNOReactants:+ NH3HCNO + NH, (HCNO + NH,) and (CH3CNO + NH3) (a) Reactants (Rl, R2); (b) transition state (TI); (c) Zwitterionic intermediateR (INT); (d) transition state (TI); (e) products: Table 1 - MNDO Structural and Energy Characteristics along the Reaction Pathway for the Reactions The C3 - Nz bond distance (denoted by R) be• rionic intermediate, !NT) and two maxima, one TI tween the carbon of l,3-dipole and the approach• leading to the formation of intermediate, and the ing nitrogen of ammonia was chosen as a reaction other 1'2 leading to the product. According to coordinate. The C3v symmetry of the C6-methyl Rothman and Lohr, these two maxima corre• group in the case of acetonitrile oxide was main• spond to the transition states as the reaction is tained while studying the acetonitrile oxide-am• continuous. The optimised geometries, shown in monia reaction system. Fig. 4, at the stationary points reveal that the INT The calculations show that at all points on the has a zwitterionic structure. reaction pathway, all the atoms except H' remain Like nitrile oxide-methanol system], the reac• in the same plane. In Table 1 is given the structu• tion proceeds in two steps. The first step involves ral characteristics and heats of formation of the interaction of carbon atom C3 of nitrile oxide reaction pathway. The reaction profiles are shown with nitrogen atom Nz of NH3, which results in in Fig. 3. On the reaction surface, there are three the formation of INT via a transition state TI at points beside the reactants and the product. reaction coordinate R = 1.88 A. This step requires These three points are: one minimum (the Zwitte- an activation energy of 28.86 kcal mol- I for 908 ~J _~I,.._I,!"~I" SHARMA & AGGARWAL: THEORETICAL STUDY OF REACTION OF NITRILE OXIDES WITH AMMONIA a. For Reaction HCNO + NH3 b. For Reaction CH3CNO +NH3 73-35 TI 10·0 70-0 11073 11 60·0 , 50.0"", ~'' AEA,=28'81 " , ieCicio.; •...... 4o-0-t (HCHI.44.4. Hlbr . 40,0 ,,, "6 Hf250'7' I '0 "0 if , bAH,. -1,30 ~ ~-o ..•..•• 30,0 ~ Q ~ a~ Reactont .ac oM I I " /I c c ICH;SCHO+ NH3) o o 28'63 ~e 20'0 AEP .-52'73 teol/.n' ~ 2(}0 •.. •..e o "6 Hf. 34,13 IS.. {l '3a •• -0 b6Hf·-1·30 :c...~ :z:::t:-~aI 10,0 ~-I 10·0 - A EP = -45,22 .·co'/llIol 0·0 0·0 3:00 2·50 2·00 ',50 ,,00 3:00 2·50 2·00 1·50 "00 . I React/on Coordinat. - R Reaction Coordinate'- R (C3-N 2)A°.l -10,0 -10' (FormamidOllime) Product -1-24 (C3-N~A· 1 (Ac.tomidoxim.) Product -,U9 Fig. 3 - Reaction profiles for addition of ammonia to nitrile oxides. HCNO and 33.10 kcal mol-I for CH]CNO. This than the reacting species by 16.94 kcal mol-1 (for step is the slowest step and hence the rate-deter• HCNO) and 21.05 kcal mol-I (for CH]CNO). mining step for the reaction. The Hammond pos• The second step involves the transfer of hy• tulatelS predicts that due to the high exothermicity drogen from Nz to Os. This then leads to the for• of the reaction (Fig. 3), TI should resemble the mation of products, formamidoxime and acetami• reactants rather than the product. The calculated doxime. The products possess Z-configuration geometry for TI (Fig. 4) with bonds R and r' is with respect to C]N4 double bond and have the consistent with this argument. The intermediate (a conformations s-cis and s-trans with respect to true energy minimum with no negative eigenvalue single bonds NzC] and N40S' as was observed ex• in the diagonalised Hessian matrix) is less stable perimentally. This step occurs very fast and re- 909 , I, lW'III'('. ,I!, j, li~ill' '.'HJ II i" ~.J ~'IUI 1.1, ,il,,,i 1"Iil ,i ''''I ~ III: I I 11'1 INDIAN J. CHEM., VOL. 26A, NOVEMBER 1987 o. For Reaction HCNO+ NH3 -.. ~ 1·041 1-169 1-191 • J + H !'OOl •. H7 ~ ~...1" ~;';0 't..•• ,. ••• 1:,111; 8610 He INT r2 Product b. For Reaction CH3CNO +NH3 H .... ~ • >I> Q o f:i~ o - ~ 1443 1·170 1189 ~ + H ~..,.H~1·007 - N 05 C N 0 IO!l2 '~. R1 R2 "H Product INT Fig. 4 - Optimised geometries (MNDO) of the reactants, the transition state (T!) for the formation of intermediate, the Zwitterionic intermediate (INT ~the transition state (T2) for the formation of product and rhe product [bond lengths in ft., and bond angles in de• gree). 910 "it II 'J' ~"f": SHARMA & AGGARWAL: THEORETICAL STUDY OF REACTION OF NITRILE OXIDES WIrn AMMONIA -.226-.398-.186.200.199.184.203.200.199.201.191-.090-.370--.444.197-.437-.354-.087-.367-.406-.343-.363-.318-.099-.405-.368-.228-.070-.412-.130-.192-.413-.320--.122-.410-.158-.125-.4Il-.132-.110-.095-.475-.429.082.472.084.089.000.176.175.093.174.096.552.083.177.094.077.578.172.107.593.076.570.180.085.563.560.070.166.062.162.157.052.082.574.183.000.086.100.098.197.016.515.095.067.076.159.181.111.262.123.118.146.094.162.120.226.212.079.133.244.158.185.134.145.139.149.076.129.148.155.163.152.IlS.Il3.132.150.157.159.117.Il4.131.116.422.094.087.407.123-.408.117.109.371.414.051.412.158.394.101.116.018.198.185.231 Table 2tHCNO-HH05N2N4H6HIH7C3Net Atomic Charges and Charge Transferred from NH3 to HCNO along the Reaction Pathway (MNDO) 1.3811.47c1.40d1.88b2.001.501.452.251.481.491.461.551.871.901.891.60ooa < For a-e see Table 1 R,A Table 3 - Net Atomic Charges and Charge Transferred from NH3 to CH3CNO along the Reaction Pathway at the Stationary Points (MNDO) R,A t--.034-.215-.007-.206-.392-.383-.228-.399--.113-.310HIO-.507-.130.207.022.076.000.086.082.051.167-.229.029.005H7.026.004.015.197.025.585.210HHN40,HIN2-.040.612.032HyHII.180.113.192Co.123.076.198.073.193.155.146.276.132.158.163.171.367.458.179.100.184.152 CO" CH,CNO C, 1.387<1.88b1.48e1.40d For a-e see Table I quires an activation energy of 1.96 and 2.17 kcal (D) Charge transfer effect mol-1 respectively for HCNO and CH3CNO. The In Tables 2 and 3 are summarised the results of exothermicity calculated for the two reactions are population analysis along the reaction coordinate -52.71 kcal mol-1 and -45.22 kcal mol-l re• and the Fig. 5 shows the progress of charge trans• spectively. No experimental data are available for fer. direct comparison. However, the calculated differ• The calculations show that the carbon C3 first ence in the barrier heights is small, which seems loses its negative charge as the nitrogen N2 of to be reasonable. NH3 approaches to it and then it starts gaining The addition of NH3 to CH3CNO (acetonitrile electrons from N 2 and transfers them to the hy• oxide) has an activation energy which is signifi• drogen, oxygen and nitrogen atoms of nitrile ox• cantly higher than that observed for the parent ide. This loss of charge is due to increase in the s• HCNO (fulminic acid). Thus, the methyl group character of R - C3 bond, conversion of partial has an overall deactivating effect and fulminic ac• C3 - N4 triple bond into double bond and forma• id is more reactive than acetonitrile oxide. The tion of lone pair of electrons on N4. In the case of structure of TI state in both the cases exhibits a fulminic acid, at reaction coordinate R = 2.00 A, very small change in the deformed angles ~, 'I the net charge transfer from C3 atom is 0.116 and LHjN2H7 or LH1N2HlO (Figs. 2 and 4). It is electrons while the net charge transfer from NH3 therefore apparent that the difference between the moiety to HCNO moiety is 0.083 electrons. This activation barriers (4.24 kcal mol- 1) for the addi• total charge of 0.199 electrons is now distributed tion of NH3 to fulminic acid and to acetonitrile over remaining three atoms of fulminic acid. Of oxide is probably due to the effect of the methyl this a major portion of the charge is acquired by group. the N 4 clearly indicating the formation of lone 911 I , 'Ii~! I .,JIH"IIIlH.duliJI'",U, I , il,,1 1,,>1,I ~ III' J I '1-'1 INDIAN J. CHEM., VOL. 26A, NOVEMBER 1987 ·1 Since there are no significant differences in charge a.For Reacllon HCNO+NH~ transfer on the INT and T2 in comparison to TI, ~ ,6 , therefore, T2 resembles the intermediate in its o " electronic structure and T2 may also be predicted Z ,5 , (.) " % ',' as zwitterion which lies on the reaction path. It is -",'4o \' .•.. ' , evident from Fig. 5 that the nucleophile NH3, ::t: C-II',', Reaction Z f '\.',', during its approach thus loses 59.3% of its nega• ~ ·3 II-II ,lJ ",,', tive charge (comprising 0.593 e-) to HCNO and ~~ "~H"" ", , 61.2% (comprising 0.612 e-) to CH3CNO, to .; 2 IntermedIOl.r-,'" form the corresponding products. ~ "- '; ·1 The calculated charge shows that the attack of ammonia (nucleophile) on flminic acid is more fa• ~ Product ~ . Heactant$ £ Formation"" ~_oc. U~ OL•• -~·I -----.--·----r---'---....,------.,"-::.ay- cile than that on acetonitrile oxide, since the elec• ',4 15 1·6 17 18 19 2·0 2·1 2·2 2·3 tronic charge on C3 atom is less in fulminic acid. Reac:tlOI\Coordinate C)- HzlR l,." It may be noted from Table 3, that the net elec• tronic charge increases by 0.131 electron on CH, group as the reaction proceeds from reactants to ;:;- '1~. I the product. It further confirms that the methyl 0' ' b.For ReactIC.II CH)CNO + NH) Z '6~ group has an overall deactivating effect. 0., " u:z: " ' It is interesting to note that N2 and H7 (e.g. ful• -o ·5 ....., , minic acid - ammonia system; see Table 2) be• :r!' CH.J ..•...... come more positive in proceeding from TI to T2 ZE.4 \ C-II' " via INT. This causes repulsion between these two ~ f \ atoms and consequently lengthening of normal :;; .3 H-II .0 - ~, N2 - H7 bond (Table 1). On .the other hand, Hs which lies away from XY-plane (Fig. 4) stops ~ ·2 Intermediate " •• Formation" suppling electrons after the reaction coordinate o~ , " ~Dg .1 H·".•••.H·' '~ , R = 1.60 A and becomes negative. At the same II "~'l.. oC time, Os gets slightly less electrons. In other U oj. ProductI '-'--- I '~.:---1-,Reactonts.,------,---r----.- words the total electronic charge gained by C 3 1·4 1·5 1·6 17 18 ',9 2·0 2·1 2'2 from the incoming nucleophile, distributes less to Rtllchon Coordinate C! - Hz (R) I A" as in comparison to H6 and N4• Therefore, only Fig. 5 - Charge transfer along the reaction pathways. H7 which lies in the XY-plane, migrates to termi• nal as of nitrile oxide and forms the amidoxime. pair of electrons on it. The total electronic charge It can be thus seen that this charge-transfer oc• curs in the same direction as is expected for a nu• spread over the N4, as and H6 atoms of fuhninic acid is 0.107, 0.034 and 0.059 electrons respect• cleophilic addition and is consistent with the ively. Thus, the present study indicates that there stereochemistry of ammonia and nitrile oxide. is a temporary reversal of polarity at carbon cen• tre in nitrile oxides on approaching the nucleo• Acknowledgement philes. One of the authors (AKA) is grateful to the CSIR, New Delhi, for the award of a senior re• In the reaction RCNO + NH3 ....•RNH2C = NOH, the TI appears at a fairly early stage in the reac• search fellowship. tion and the main effect in passing from the react• ant to TI is the transfer of 0.174 and 0.192 elec• References trons from NH3 to HCNO and CH3CNO respect• 1 Sharma K K & Aggarwal A K, IntJ Quantum Chern, 30 (1986) 213. ively. This net charge transfer increases in going 2 Dignam K J, Hegarty A F & Quain P L, ] chern Sac, Per• from R1 + R2 to intermediate (INT) via T1 by kin Trans, 2 (1977) 1457. 0.570 and 0.585 electrons. Therefore, the total 3 Dignam K J & Hegarty A F, ] chern Sac, Chern Com• net charge transfer on INT from Tl is 0.396 and mun, (1976) 862. 0.393 electrons respectively. Out of this, the main 4 Gozlan H, Michelot R & Rips R, Tetrahedron Leu, 11 (1975) 859. effect is on C3 which gains an electronic charge of 0.334 in case of fulminic acid and 0.328 in case 5 Gozlan H, Michelot R, Riche C & Rips R, Tetrahedron. 33 (1977) 2535. of acetonitrile oxide. At T2, the net charge trans• 6 Dondoni A, Gilli H & Sacerdot M, ] chern Sac, Perkin fers are 0.593 and 0.612 electrons respectively. Trans, 2 (1976) 1036. 912 1-.~~, II"~" I" SHARMA & AGGARWAL: THEORETICAL STUDY OF REACTION OF NITRILE OXIDES WITH AMMONIA 7 Hall D & Llewellyn F J, Acta Crystallogr, 18 (1965) 955; 13 McIver (Jr) J W & Komornicki A, J Am chern Soc, 94 9(1956) 108. (1972) 2625. 8 Dignam K J, Hegarty A F & Quain P L, I org Chern, 43 14 Rothman M J & Lohr L L Jr., Chern phys Lell, 70 (1980) (1978) 388. 405. 9 Dewar M J S & Thiel W, I Am chern Soc, 99 (1977) 15 Dewar M J S & Thiel W, J Am chern Soc, 99 (1977) 4899. 4907. 10 Fletcher R & Powell M J D, Comp J, 6 (1963) 163; Da• 16 Winnewisser M & Bondenseh H K, Z Naturforch, 22A vidonWC, Compl, 10(1968)406. (1967) 1724; Winnewisser B P, Winnewisser M & 11 Thiel W, Weiner P, Stewart J & Dewar M J S, MNDO Winther F, J mol Spec, 51 (1974) 6~. Program No 353, Quant Chern Prog Ex Bulletin, 17 Padwa A, 1,3-Dipolar cycloaddition chemistry (Wiley, 1981. New York) 1977, pp 28. 12 Muller K,AngewChem IntEdnEng, I (1980) 19. 18 Hammond GS,JAm chern Soc, 77(1955)334. 913