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Kinetic and Equilibrium Acidities for Nitroalkanes J Kinetic and Equilibrium Acidities for Nitroalkanes J. Org. Chem., Vol. 43, No. 16, 1978 3107 12, 131 (1962). (34) F. Klivenyi, Magy. Kem. Folyoiraf, 64, 121 (1958); Chem. Abstr., 54, 16416e (22) H. R. Slagh, U.S. Patent 2 632 776; Chem. Abstr., 48, 1412 (1954). (1959). (23) M. M. Holleman. Recl. Trav. Chim. fays-Bas, 23, 299 (1904). (35) J. E. Dunbar and J. H. Rodgers, J. Org. Chem,, 31, 2842 (1966). (24) V. M. Rodionov, I. M. Machinskaya, and V. M. Belikov, Zh. Obshch. Khim., (36) T. Mukaiyama, TetrahedronLett., 5115 (1970). 18, 917 (1948); Chem Abstr., 43, 127 (1949). (37) W. E. Truce, T. C. Klinger, J. E. Parr, H. Feuer, and D. K. Wu, J. Org. Chem., (25) N. Kornblum, H. 0. Larsen, R. K. Blackwood, D. D. Mooberry, E, P. Oliveto. 34, 3104 (1969). and G. E. Graham, J. Am. Chem. SOC.,78, 1497 (1956). (38) R. R. Dreisbach and R. A. Martin, lnd. Eng. Chem., 41, 2876 (1949). (26) A. A. Griswold and P. 13. Starcher, J. Org. Chem.. 30, 1687 (1965). (39) J. G. Miller and H. S. Angel, J. Am. Chem. Soc., 68, 2358 (1946). (27) N. KornblumandG. E. Graham, J. Am. Chem. Soc., 73,4041 (1951). (40) N. Kornblum, 6. Taub, and H. E. Ungnade, J. Am. Chem. SOC.,76, 3209 (28) J. P. Kispersky, H. B. Hziss, and D. E. Holcomb, J. Am. Chem. Soc., 71, 516 (1954). (1949). (41) A. P. Howe and H. B. Hass, lnd. Eng. Chem., 38, 251 (1946). (29) (a) L. Henry, Bull. Aca89.R. Belg., 36, 149 (1898); J. Chem. Soc., Abstr., (42) F. T. Williams, Ph.D. Thesis, The Ohio State University, Columbus, Ohio, 251 (1899); (b) N. Kornblum and H. E. Ungnade, Org. Synth., 38, 75 1958, p 65. (1958). (43) J. V. Braun and 0. Kruber. Ber. Dtsch. Chem. Ges., 45, 395 (1912). (30) D. E. Pearson and J. D. Bruton, J. Org. Chem., 19, 957 (1954). (44) L. Henry, Rec. Trav. Chim. fays-Bas, 16, 193 (1897). (31) L. I. Smith and E. R. Rogier, J. Am. Chem. Soc,, 73, 4047 (1951). (45) J. V. Braun, H. Deutsch, and A. Schmatiock, Ber. Dtsch, Chem. Ges., 45, (32) J. D. Roberts and V C. Chambers, J. Am. Chem. SOC., 73, 3176 1252 (1912). (1951). (46) N. Kornblum and W. M. Weaver, J. Am. Chem. Soc., 80,4333 (1958). (33) H. Lecher and F. Holschneider, Ber. Dtsch. Chem. Ges., 57, 755 (47) J. Troger and E. Nolte, J. frakt. Chem., [2], 101, 136 (1920). (1924). (48) K. v. Auwers and L. Harres, Ber. Dtsch. Chem. Ges., 62, 2287 (1929). Kinetic and Equilibrium Acidities for Nitroalkanes F. G. Bordwell,* John E. Bartmess, and Judith A. Hautalal Department of Chemistry, Northwestern Uniuersity, Euanston, Illinois 6020I Received March 14,1977 Rates of deprotonation for 20 nitroalkanes, G(CHz),NOZ, where n is 1,2, or 3, catalyzed by lyate ion or by pyri- dine were measured in 50% (v/v) MeOH-H20. The rates were correlated reasonably well by the Taft relationship, but this is believed to be fortuitous for n = 1 or 2. A Brdnsted plot for lyate rates vs. equilibrium acidities for n = 3 gave a slope of 1.67 and for pyridine rates gave a slope of 1.89. Rates of deprotonation by lyate ion of seven secon- dary nitroalkanes, RR’CHN02, with R or R’ = Me, Et, Pr, i-Pr, or c-Pr, were measured in 50% (v/v) MeOH-HZO. Changes in R (or R’) caused larger effects in kinetic acidities than in equilibrium acidities; these effects were fre- quently in inverse directions. A three-step mechanism involving a singly H-bonded anion intermediate or a virtual intermediate is postulated to account for the large kH/kD isotope effects and “anomalous” Bransted coefficients observed for the deprotonation of nitroalkanes in protic solvents. Six examples are given from kinetic and equilibri- um acidity data where the order of polar effects is PhS > PhO, which is opposite to the order of Taft UI constants. Although there is a wealth of information concerning 95% confidence level). Points for GCH2CHzN02 and rates of deprotonation of simple nitroalkanes with varied bases GCH2N02 compounds vs. U*CH~Gand CT*G, respectively, are (HO-, AcO-, pyridine, et^.),^-^ relatively little information also included in Figure 1, but were not used in the least- concerning the effect of introducing heteroatom substituents squares plot to determine p*. into the alkyl groups is available. We now present data for The rates of deprotonation of the G(CHz),N02 compounds rates of deprotonation of nitroalkanes, G(CHz),N02, where with pyridine base in 50% MeOH-H20 were determined by G is a heteroatom substituent and where n = 1,2, or 3, with a buffer dilution method, using triiodide ion as a scavenger lyate ion in 50% (v/v) MeOH-H20 and with pyridine in 50% for the nitronate ion6a(Table I). The zero-order disappearance (v/v) MeOH-H20. These results, together with those on the of triiodide is the actual kinetic variable. Iodination of the effect of alkyl substitution into nitromethane, are then com- nitroalkanes does not go to completion,6b but is extensive pared with the equilikirium acidity data5 for these compounds enough to allow successful measurement of rate constants. For in the same solvent. 3-substituted-l-nitropropanes,GCH&H&H2N02, with G = H, Ph, OH, OPh, S02Ph, and CN, a Taft plot gave p* = 2.27 Results & 0.26 (r = 0.957; R2 = 0.916; SD = f0.62 at 92% confidence Rates of deprotonation by lyate ion in 50% (v/v) metha- level). Points for 1,3-dinitropropaneand 5-nitro-2-pentanone nol-water at 15 “C of 20 nitroalkanes of the type G(CH2),- were not included because of complications due to side reac- Nos, where n is 1 2, or 3 and G is hydrogen, methyl, or a tions. The distribution of the other points (Table I) along the functional group, were measured by observance under line was similar to that shown in Figure 1. pseudo-first-order conditions of the appearance of nitronate A Br@nstedplot (Figure 2) for lyate ion deprotonation in ion absorbance at 225-240 nm. Excellent kinetics were ob- 50% MeOH-H20 (at 15 “C) vs. equilibrium acidities in 50% tained in most instances with correlation coefficients of X.999 MeOH-H20 (at 25 “C) for GCH~CH~CH~NOZcompounds, for each run (Table I). The behavior of 3-chloro-1-nitropro- with G = H, Ph, OH, COCH3, OPh, SPh, SOzPh, and CN, gave pane was exceptional in that the infinity absorbance slowly a = 1.67 f 0.19 (r = 0.957). Since the temperature dependence decreased with time, probably due to cyclization to form is- for pK’s for nitroalkanes is known to be small,7 and should be oxazoline oxide. Lyate rates were also measured for a number similar for a series such as G(CH2)3N02, the fact that the ki- of secondary nitroalkanes, RR’CHN02. The data are sum- netic and equilibrium measurements were made at tempera- marized in Table 111. tures 10 “C apart should not affect CY appreciably. The A Taft plot (Figure 1) constructed from the lyate rates for Br@nsteda for a plot of pyridine deprotonation rates in 50% 3-substituted-l-nitropropanes,G(CH2)3N02, vs. u*cH*,;H~G, MeOH-H20 (at 25 “C) vs. pK’s in 50% MeOH-H20 (at 25 “C) with G = H, Ph, OH, SPh, COCH3, OPh, C1, SOzPh, and CN, was 1.89 f 0.19 (r = 0.965). gave p* = 2.09 f 0.17 (r = 0.975; R2 = 0.950; SD = f0.39 at The correlations of the (calculated) rates of protonation of 0022-3263/78/1943-3107$01..00/00 1978 American Chemical Society 3108 J. Org. Chem., Vol. 43, No. 16, 1978 Bordwell, Bartmess, and Hautala Table I. Deprotonation Rates of Nitroalkanes, GCHzN02, by Lyate Ion and Pyridine in 50% (v/v) Methanol-Water registry h, lOjk, G no. M-1 S-ln k, M-1 S-lb t -Bu 34715-98-5 0.63 0.182 i-Pr 625-74-1 3.3 1.35 n-Pr 627-05-4 4.6 2.68 Et 108-03-2 4.7 2.17 Me 79-24-3 5.5 2.83 (CH2)2Ph 22818-69-5 10.9 4.08 c-Pr 2625-33-4 10.6 3.95 Et ,,&'e (CHzhOH 25182-84-7 15.4 6.25 ~r *H (or CH,) (CH2)zCOCH3 22020-87-7 16.4 CHzPh 6125-24-2 16.3 6.05 (CHz)zSPh 66291-17-6 27.8 12.2 (CHz)20Ph 66291-15-4 21.3 9.61 CHPh2 5582-87-6 36.6 c.0 -+ (CHdzCl 16694-52-3 43.8 (CHz)zSOzPh 66291-13-2 58.5 24.6 .L-Bu (CHdzCN 58763-41-0 45.2 21.6 I H 75-52-5 30' 8.04 _--_-4--- -i-,-- __---/ -0.3 -1?.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 (CHdzNOz 6125-21-9 68 CHzOH 625-48-9 79.3 11.4 .I, CH!CH!G (e)Or :EHIG (A)or (.) Ph 622-42-4 144 147 Figure 1. Plot of the logarithm of the rates of deprotonation by lyate a At 15 "C, with lyate ion as the base; reproducible to 321%. At ion in 50% MeOH-H20 at 15 "C for 3-substituted 1-nitropropanes, 25 "C, with pyridine as the base; reproducible to 55%. Extra- GCHZCHZCH~NO~,vs.
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