Elimination Of HCN Research Articles

Very low-pressure pyrolysis (VLPP) of 3-chloropropionitrile

The thermal decomposition of 3-chloropropionitrile has been investigated over the temperature range 942–1152 K using the technique of very low-pressure pyrolysis (VLPP). The experimental results are consistent with the reaction proceeding via the unimolecular elimination of HCl CH2ClCH2CN → C2H3CN + HCl. The high-pressure Arrhenius parameters obtained via the application of RRKM theory are given by log (k∞/s–1)=(13.2 ± 0.3)–(241.0 ± 4 kJ mol–1)/2.3 RT.In contrast to its decomposition in a conventional static system, no radical reactions occur under VLPP conditions. No evidence could be found for the unimolecular elimination of HCN. When compared with the extant kinetic parameters for the unimolecular elimination of HCl from ethyl chloride, the results show that β-cyano substitution has a retarding effect on the rate of HCl elimination. This is consistent with a polar transition state.

Imine chemistry I. A new route to pyrroles and related compounds from imines and 2‐chloroacrylonitrile

AbstractThe Michael addition of 2‐chloroacrylonitrile to imines (potential enamines) and the subsequent elimination of HCN produced pyrroles and condensed pyrroles.

Mass spectrometry of 3‐substituted 4‐hydroxyisoquinolines and their derivatives

AbstractUnder electron impact, 3‐aryl‐4‐hydroxyisoquinolines form [M – H]+, [M – CO]+ and [M – H – CO]+ ions with a subsequent elimination of HCN or CH3CN. A cyclic structure for the [M – H]+ ion is suggested. The primary act of fragmentation of the corresponding methyle ether derivatives is the loss of CH3⋅, as well as H⋅; the further fragmentatio is similar to that described above. It has been established that the unusual [M – H]+, [M – OH]+ and [M – CH5⋅]+ ions are formed when 8 fragments. Fragmentation schemes for all compounds are proposed based upon high resolution mass spectra and deuterated analogues.

Very low‐pressure pyrolysis (VLPP) of alkyl cyanides. II. n‐propyl cyanide and isobutyl cyanide. The heat of formation and stabilization energy of the cyanomethyl radical

AbstractThe very low‐pressure pyrolysis (VLPP) technique has been used to study the pyrolysis of n‐propyl cyanide over the temperature range of 1090–1250°K. Decomposition proceeds via two pathways, C2C3 bond fission and C3C4 bond fission, with the former accounting for >90% of the overall decomposition. Application of unimolecular reaction rate theory shows that the experimental unimolecular rate constants for C2C3 fission are consistent with the high‐pressure Arrhenius parameters given by where θ=2.303RT kcal/mole. The activation energy leads to DH2980[C2H5CH2CN]=76.9±1.7 kcal/mole and ΔH(ĊH2CN, g)=58.5±2.2 kcal/mole. The stabilization energy of the cyanomethyl radical has been found to be 5.1±2.6 kcal/mole, which is the same as the value for the α‐cyanoethyl radical. This result suggests that DH[CH2(CN)H] ∼ 93 kcal/mole, which is considerably higher than previously reported. The value obtained for ΔHƒ0(ĊH2CN) should be usable for prediction of the activation energy for C2C3 fission in primary alkyl cyanides, and this has been confirmed by a study of the VLPP of isobutyl cyanide over the temperature range of 1011–1123°K. The decomposition reactions parallel those for n‐propyl cyanide, and the experimental data for C2C3 fission are compatible with the Arrhenius expression A significant finding of this work is that HCN elimination from either compound is practically nonexistent under the experimental conditions. Decomposition of the radical, CH3CHCH2CN, generated by C3C4 fission in isobutyl cyanide, yields vinyl cyanide and not the expected product, crotonitrile. This may be explained by a radical isomerization involving either a 1,2‐CN shift or a 1,2‐H shift.

Farbstoffe durch Amin?HCN-Austauschreaktion am 2-Dicyanmethylen-1,3-indandion, 2. Mitt.

Further examples for the amine—HCN-exchange reaction of dieyanomethylene-1.3-indandione are given. With aminonaphthoquinones and aminoanthraquinones, resp., thermolabile adducts are isolated, which eliminate HCN to anthrachinoyl-amino-dioxo-indanyliden-acetonitriles and dioxo-indanylidene-naphthochinoyl-amino-acetonitriles, resp. The reaction of dicyanomethylene-1.3-indandione with amino-pyrazoles yields indeno-pyrazolo-pyridines, formed by elimination of HCN and condensation. In the presence of piperidine or morpholine malononitrile is added to dicyanomethylene-indandione and orange-red amino-dioxo-indanylidene-piperidino- (morpholino-) propene-dicarbonitriles are formed.

Use of metastable peak shapes in determining ring size in cyclic rearrangements in the mass spectrometer

AbstractA general method is described in which the mechanism of a reaction occurring in the ion source is inferred from the kinetic energy release accompanying further fragmentation of metastable product ions. In several cases the probe reaction occurred competitively by two mechanisms, and if high energy resolution is available this allows the detailed metastable peak shapes and not merely the average kinetic energy released, to be used to characterize the product ion formed in the fast (ion source) reaction. It is found that most substituted benzaldoxime O‐methyl ethers undergo HCN elimination via a five‐centered methoxyl transfer in the ion source, but that the p‐methoxy substituted compound reacts through both a four‐ and a five‐membered cyclic intermediate. The slow reactions of the corresponding metastable ions occur predominantly through a four‐centered transition state in the p‐methoxy compound and probably through both four‐ and five‐membered intermediates for the less strongly electron donating substituents. The fraction of the excess energy of the products is higher than expected from a consideration of energy partitioning data for other systems involving activated complexes of comparable tightness.

Free-radical substitution in aliphatic compounds. Part XXVII. Chlorination and bromination of 1-cyanobutane and cyanocyclobutane

1-Cyanobutane and cyanocyclobutane have been chlorinated and brominated in the gas phase over a wide range of temperatures. The results for 1-cyanobutane are compared with previous halogenations of 1-substituted n-butanes. The chlorination of cyanocyclobutane gives a very high trans/cis ratio for the 1-cyano-2-chlorocyclobutane and quite a high trans/cis ratio for the 1,3-product. This is interpreted in terms of an interaction between the π-orbitals of the cyano-group and the half-filled 2p2 atomic orbital of the radical site. The bromination of cyanocyclobutane is accompanied by a small amount of elimination of HCN; this reaction is increased by addition of HBr or by an increase in the surface area.

Mass spectra of 1,2,4‐triazoles—II: Alkyl 1,2,4‐triazoles

AbstractThe mass spectra of monomethyl 1,2,4‐triazoles contain fragment ions produced by specific cleavage of the heterocyclic ring. A major fragmentation from many molecular ions involves the elimination of HCN, but loss of N2 is either very small or completely absent. No N or H scrambling occurs within the triazole ring system, as evidenced by labelling studies. The loss of a hydrogen atom from the molecular ions of 3‐alkyl‐1,2,4‐triazoles (alkyl ⩾ C2H5) originates from hydrogens attached to the β carbon and nitrogen atoms.

E1cB eliminations. Substituent and solvent effects on the E1cB elimination of the second type from 2-aryl-1,1,2-tricyanopropanes

Tri-n-butylamine-promoted elimination of HCN from 2-aryl-1,1,2-tricyanopropanes shows ‘catalysis’ by the amine in chloroform and in acetonitrile. The reaction is of first order in the amine at low amine concentrations and zeroth order at high amine concentrations. In the latter region the reaction is faster in chloroform than in acetonitrile, the Hammett ρ+ values being –0·36 and kH/kD= 1·0 ± 0·08. The reaction is discussed in terms of nonsteady-state formation of the conjugate base of 2-aryl-1,1,2-tricyanopropane, which leads to complete ionisation (E1cB of the second type) at the high amine concentrations with rate-determining C–CN bond cleavage. In chloroform (and in some cases in acetonitrile) the kinetics fit the ion-pair variant (E1cB)ip.

Formal 1,1-elimination of hydrogen cyanide from o-nitrobenzyl cyanide under electron impact

The elimination of HCN from the molecular ion of o-nitrobenzyl cyanide under electron impact is shown by deuterium labelling to take place with the abstraction of one of the benzylic hydrogens. This is the first case of a specific 1,1-elimination. o-Nitrobenzyl chloride and o-nitrobenzyl alcohol do not undergo similar eliminations.

Studies on the mass spectra of 6‐methylthiopurine and its C‐and N‐methyl derivatives

Abstract6‐Methylthiopurines which bear a 9‐NH‐ or a 9‐NCH3‐group (class A) form an [M—1]‐ion with much higher abundance than do the 1‐, 3‐, or 7‐methyl derivatives (class B). The higher stability of the [M—1]‐ion in class A may be explained by ring closure to N‐7.Methyl radicals are cleaved from N‐, but not from S‐ or C‐methyl groups, with the exception of the 7‐methyl derivative, in which the S‐CH3‐group can also split off a methyl radical. The methylthio group may lose all of the following fragments: S, SH, SCH, SCH2 and SCH3. In the remaining purine skeleton, in general first the pyrimidine and subsequently the imidazole ring breaks down with elimination of HCN.

E1cB eliminations. Part V. Two types of E1cB reaction in the amine-catalysed elimination of HCN from 2,6-dimethyl-4-(ααββ-tetracyanoethyl)aniline in chloroform

Amine-catalysed elimination of HCN from 2,6-dimethyl-4-(ααββ-tetracyanoethyl)aniline (I) in chloroform goes to completion even if [I] > [Amine]. With Et3N and Bun3N the reaction is of zero order in both (I) and the amine within a run, and of the first order in the amine for different runs when [Amine] < [I]. For eight other amines with lower pKb′s the reaction is of the second order. The kH/kD values for all the amines are 1·0 ± 0·06. The reaction of Et3N and Bun3N is discussed in terms of ‘E1cB of the second type’ through ion-pairs, where almost complete neutralisation of (I) is followed by a rate-determining trialkylammonium ion-assisted elimination of CN– from the intermediate carbanion–ammonium ion pair. The reactions with the other amines give less neutralisation of (I) and are discussed in terms of the ‘pre-equilibrium’E1cB mechanism. The expulsion of CN– is also assisted by the ammonium ion, probably within the ion pairs.

The problem of the azatropylium ion: Hydrogen elimination from the molecular ion of γ‐picoline

AbstractComparison of the mass spectrum of γ‐picoline with that of analogues, specifically deuterated in the methyl group, the ring or both, has shown that the molecular ion loses the α,β and methyl hydrogen atoms (ω‐hydrogen') in the ratio 1.43: 1: 1. 13. The same trend is found for the elimination of HCN from the molecular ion. Moreover, a value of 1.52 is found for the isotope effect, expressing the favoured loss of H over D, irrespective of its position.

Mass Spectra of Organometallic Compounds. V. Some Π-Cyclopentadienyl Derivatives Not Containing Carbonyl Groups

The mass spectra of the following compounds are reported: (1) the π-eycloheptatrienyl derivatives C5H5 MC7H7, ( M = V and Cr); (2) the π-pyrrolyl derivative C5H5FeC4H4N; (3) the ethylene derivative C5H5Rh(C2H4)2; (4) the 1,5-cyclooctadiene derivatives C5H6 MC8H12 ( M = Rh or Ir); (5) the trimethylplatinum derivative (CH3)3PtC5H5; (6) the nickel and palladium complexes C3H5PdC5H5, C10H12OCH3PdC5H5, and C5H5NiC13H17. The following features of particular interest were observed: (1) evidence for elimination of neutral C6H6 fragments from the C5H5- MC7H7 compounds; (2) evidence for elimination of C2H2, HCN, C2H2N, C4H4N, and Fe fragments from the parent ion of C5H5FeC4H4N; (3) evidence for stepwise elimination of ethylene ligands from C6H5Rh(C2H4)2; (4) evidence for relatively weak metal–π-cyclopentadienyl bonds in the nickel and palladium derivatives.

Alkaloids of the Australian Rutaceae: Halfordia scleroxyla. III. Mass spectrometry of halfordinol and related oxazoles

Comparative studies by mass spectrometry of halfordinol [2-(3-pyridy1)-5-(4-hydroxyphenyl)oxazole] and other derivatives of the new oxazole alkaloid N-methylhalfordinium chloride with model aryloxazoles confirmed the structure of the alkaloid. One of the main features of the decomposition of 2,5-diaryloxazole ions in the mass spectrometer involved a novel concerted elimination of HCN and CO. A mechanism has been proposed for this and other reactions of oxazole ions, including those of 4,5- and 2,4-diphenyl derivatives.

Structure Analysis of High Molecular Organic Compounds with their Fragment Ions produced by Electron Impact

The mass spectra of 8, 8-dicyanoheptafulvene and its derivatives, which are considered to belong to a nonbenzenoid aromatic compound, were measured. The high degree of aromaticity of8, 8-dicyanotheptafulvene was made clear by masss pectrometry. Low mass regions of dicyanoheptofalvene showed the elimination of HCN from parent ion and rearrangement to phenvlpropiolonitrile ion. The mass spectra of methoxy-dicyanoheptafulvenes showed fragmentation quite different from that 8, 8-dieyanoheptafulvenes. The structure and fragmentation processes of dieyanoheptafulvenes were discussed.

Studies in Mass Spectrometry. II. Random Hydrogen Rearrangement in Aromatic Molecular Ions

To provide data for investigations by, inter alia, mass-spectrometric methods into the deuterium exchange of the aromatic hydrogen of some coal fractions, a study was made which confirmed the occurrence of completely random hydrogen rearrangement prior to or during the elimination of C2H2 in the molecular ions of benzene-1,2,3-d3, benzene-l,3,5-d3, naphthalene-1,2,3,4-d4, naphthalene-1,4,5,8-d4, and phenanthrene-9,10-d2, and in the phenyl ions derived from o-bromobenzene-d, m-bromobenzene-d, and p-chlorobenzene-d, Similar but incomplete hydrogen rearrangement was found to occur in the molecular ion of carbazole-N-d prior to or during elimination of HCN. Such rearrangements, for which mechanistic considerations are presented, must be taken into account when the mass spectra of deuterium-substituted aromatic compounds are being interpreted.