Base-catalysed Decomposition Research Articles

Kinetics of conversion of dihydroxyacetone to methylglyoxal in New Zealand mānuka honey: Part V - The rate determining step.

Monomer formation from dimeric DHA has previously been suggested as the rate-determining step in formation of methylglyoxal, the bioactive component in mānuka honey. This step was studied by 1H NMR in DMSO‑d6. First order reaction rate was 3.31 × 10-3 ± 9.1 × 10-4 min-1. Upon titration with D2O, little change was observed until ∼15 mass% whereupon an exponential increase in rate occurred until indistinguishable from the rate observed in water. Acid or base caused rate accelerations. Theoretical modelling confirmed the existence of acid and base-catalysed mechanisms for dimer decomposition and the structures of two intermediates observed. In honey it is likely the base-catalysed decomposition predominates with water as catalyst but there is little rate acceleration at the levels of water present normally in honey however a small increase in the mass% of water in the honey could cause significant rate acceleration of dimer decomposition and hence formation of methylglyoxal.

Base-catalysed decomposition of polychlorinated biphenyls in transformer oils by mixture of sodium hydroxide, glycerol and iron.

In this research, a method based on base-catalysed decomposition (BCD) was developed using sodium hydroxide and glycerol for dechlorination of transformer oils with low levels of polychlorinated biphenyls (PCBs). PCB removal and dechlorination efficiencies were measured by gas chromatography and the silver nitrate titration method, respectively. PCB dechlorination and removal efficiencies after 4 h at 250°C and in the presence of iron were 97.4% and 99.8%, respectively. However, in the absence of iron the same efficiencies were calculated to be 79.4 and 99.7%, respectively. The dielectric loss factor of oil refined at 250°C was 0.0064 and did not meet the required standards to be reused in the transformers. However, that refined at 200°C satisfied the standards with acceptable conversion rates. Use of iron, besides increasing conversion rates, changed the mechanism of the reaction from nucleophilic substitution to a combination of hydrodechlorination and nucleophilic substitution. In the presence of iron, highly chlorinated PCBs were converted to less chlorinated PCBs, and this caused the concentration of less chlorinated PCBs to reach a peak and then decline thereafter. The production of PCB 36 confirmed this. However, in the absence of iron particles, all changes in the PCB concentration curves were downward.

N-heteroatom substitution effect in 3-aza-cope rearrangements

BackgroundThe nature of the heteroatom substitution in the nitrogen of a 3-aza-Cope system is explored.ResultsWhile N-propargyl isoxazolin-5-ones suffer 3-aza-Cope rearrangements at 60°C, the corresponding N-propargyl pyrazol-5-ones need a higher temperature of 180°C for the equivalent reaction. When the propargyl group is substituted by an allyl group, the temperature of the rearrangement for both type of compounds is less affected by the nature of the heteroatom present. Treatment with a base, such as ethoxide, facilitates the rearrangement, and in the case of isoxazol-5- ones other ring opening reactions take precedence, involving N–O ring cleavage of the 5-membered ring. However when base-catalysed decomposition is prevented by substituents, products arising from a room temperature aza-Cope rearrangement are isolated. A possible mechanistic pathway based on free energies derived from density functional calculations involving cyclic intermediates is proposed.ConclusionsThe nature of the heteroatom substitution in the nitrogen of a 3-aza-Cope system leads to a remarkable difference in the energy of activation of the reaction.

Acidic and basic properties of nitramide, and the catalysed decomposition of nitramide and related compounds: an ab initio theoretical investigationElectronic supplementary information (ESI) available: selected geometrical parameters, energies and zero point energies of nitramide 1, its aci-nitro isomers 4a–d, anion 7, and molecular complexes MC1 and MC1′ calculated at MP2/6-31G** and MP2/6-311++G** levels of theory. See http://www.rsc.org/suppdata/p2/b1/b105074p/

Deprotonation from nitrogen of the aci-nitro tautomer (4) of nitramide (1) has been shown to give an anion which does not correspond to an energy minimum on the potential energy surface. The base-catalysed decomposition of nitramide via this tautomer, therefore, occurs by an enforced concerted mechanism which, on the basis of previously reported experimental results, is deduced to be highly asynchronous. Protonation of 4 on the hydroxy also leads to an ion which spontaneously fragments, consequently the acid-catalysed decomposition of 1via4 also involves concerted proton transfer and fragmentation. The uncatalysed decomposition of nitramide through the same tautomer 4 is also concerted, and the mechanism through a cyclic transition structure involving two water molecules is shown to be more favourable than a cyclic concerted mechanism involving a single water molecule. Structures and energies of all relevant species have been calculated and shown to be in good agreement with experimental results where these are available.

Antitumour imidazotetrazines. Part 39. Synthesis of bis(imidazotetrazine)s with saturated spacer groups

Bis(imidazotetrazine)s (16), related in structure to the antitumour agents mitozolomide (1a) and temozolomide (1b), but linked through the N(3)–N(3′) atoms of the imidazo[5,1-d][1,2,3,5]tetrazine ring-systems, are prepared by interaction of 5-diazoimidazole-4-carboxamide (8) and diisocyanates (15). The presence of the polymethylene linker with/without sulfur and oxygen heteroatoms does not substantially affect the acid stability, base-catalysed decomposition, antitumour activity or DNA base alkylation preference characteristic of the unlinked imidazotetrazines mitozolomide and temozolomide.

Trichlorosilylation of chlorogermanes and chlorostannanes with HSiCl 3/Net 3 followed by base-catalysed formation of (Me 3Ge) 2Si(SiCl 3) 2 and related branched stannylsilanes

Chlorotrimethylgermane 1 and dichlorodimethylgermane 4 react with trichlorosilane and triethylamine to provide trichlorosilylgermanes Me 4− n Ge(SiCl 3) n ( n=1: 2; n=2: 5) in fair yields, as distillable liquids. The formation of 2 is followed by base-catalysed decomposition reactions leading to novel solid (Me 3Ge) 2Si(SiCl 3) 2 3. Chlorotrialkylstannanes 6a– c ( 6a: R=CH 3, 6b: R=C 2H 5, 6c: R= n-C 4H 9) react with trichlorosilane and triethylamine providing the branched silylstannanes (R 3Sn) 2Si(SiCl 3) 2 7a– c and traces of silylstannanes R 3SnSiCl 3 8a– c. Only 7a was isolated in a pure state. Heating 7a or crude 7b and 7c with benzyl chloride leads to the formation of benzyltrichlorosilane ( 10). The constitution of compounds 2, 3, 5 and 7a was confirmed by MS, NMR and analytical data. The structures of C 6D 6-solvated 3 and C 6H 6-solvated 7a were determined by X-ray diffraction, and shown to be isotypic.

Crosslinkable poly(phenylene oxide) containing pendent 1,2-diphenylcyclopropane groups

Crosslinkable poly(phenylene oxide)s containing pendent 1,2-diphenylcyclopropane groups have been synthesized by oxidative polymerization from four new phenols containing the 1,2-diphenylcyclopropane group. The monomers were prepared by base-catalysed decomposition of the corresponding hydroxy-substituted 3,5-diphenyl-2-pyrazolines, which were the products of the reaction between hydroxy-substituted chalcones and hydrazine monohydrate. Characterization of and crosslinking studies on these polymers were carried out utilizing differential scanning calorimetry, thermogravimetric analysis, gel permeation chromatography and nuclear magnetic resonance. The polymers can be thermally cross-linked when heated to 350°C and the glass transition temperatures (Tg) of the polymers increase after crosslinking. The resulting crosslinked networks are insoluble in all solvents examined. Thermogravimetric analysis shows that no significant weight loss accompanies the crosslinking reaction.

Reactions proceeding via the reactive intermediate α-vinyl- p-xylylene. Contrasting orientations in the formation of cyclic dimers and polymer

α-Vinyl- p-xylylene ( 16) has been shown to be an intermediate in the base-catalysed decomposition of both p-allylbenzyltrimethylammonium bromide ( 17) and p-methylcinnamyltrimethylammonium bromide ( 19). Cyclic dimers ( 28) and ( 29) ( EE and ZZ isomers, respectively) are produced via the conjugatively extended vinyl head h′ to head h′ and tail to tail bond-forming reactions, which accompany a copolymer formed mainly via the contrasting head (vinyl-substituted head h and h′) to tail linking of α-vinyl- p-xylylene.

Reactions proceeding via the reactive intermediate α-phenyl- p-xylylene. Contrasting orientations in the formation of cyclic trimers and polymer

α-Phenyl- p-xylyene ( 7) has been shown to be an intermediate in the base-catalysed decomposition of both p-benzylbenyltrimethylammonium bromide ( 11) and p-methylbenzhydryltrimethylammonium bromide ( 12). All the possible cyclic trimers of unsymmetrical linking are formed (i.e. phenyl-substituted head h to h and tail to tail links), which accompany a polymer formed mainly via the contrasting head to tail linking of α-phenyl- p-xylylene.

ChemInform Abstract: Synthesis of NH Aldimines and Derivatives by Spontaneous and Base‐catalysed Decomposition of Oxaziridines.

AbstractDie aus den Iminen (I) erhaltenen Oxaziridine (IIb) ‐(IIh) zerfallen in die im Formelschema aufgeführten Produkte, wobei z.T. auch Aldehyde des Typs Rl‐CHO gebildet werden.

Stereochemical and mechanistic aspects of the base-catalysed decomposition of N-alkyloxaziridines to form NH ketimines

The synthesis of a new range of oxaziridines (18)–(23), (30)–(35) by peracid oxidation of diaryl ketimines and aryl aldimines is reported. Relatively stable NH ketimine products (24)–(27) have been isolated from base-catalysed decomposition of the oxaziridines (18)–(20), (30)–(35) and a primary kinetic isotope effect (ca. kH/kD 6.0) was observed during decomposition of the oxaziridine trans-(31). The trans-oxaziridines (31)–(35) were found to decompose at a faster rate than the corresponding cis isomers. The relative rates of base-catalysed decomposition of oxaziridine stereoisomers are consistent with a mechanism involving an α-C–H proton abstraction mechanism.

The synthesis of NH aldimines and derivatives by spontaneous and base-catalysed decomposition of oxaziridines

A range of oxaziridines containing N-methylene substituents has been synthesized by peracid oxidation of the corresponding fluorenylidene N-alkylamines. Spontaneous and tertiary amine base-catalysed decomposition of the oxaziridines into unstable NH aldimines and derivatives was observed. Acrylaldehyde, 2-methylacrylaldehyde, and benzaldehyde NH imines have been identified as initial products from decomposition of the corresponding oxaziridines. 2,4,6-Trialkylhexahydro-1,3,5-triazines, N,N′-dialkylidene-1,1 -diaminoalkanes, N,N′-diarylidene-1,1 -diaminoalkanes, and N-iso-butylidene-2-methylpropenylamine were among the isolated products formed via the undetected alkyl aldehyde NH imines resulting from oxaziridine decomposition.

An investigation of the thermal decomposition of the methohydroxides and methodeuterio-oxides of some 5-N,N-dimethylaminopent-1-enes

The base-catalysed thermal decomposition of a number of quaternary bases of the type (R1)2CCHC(R2)2C(R3)2CH2NMe3X–(R1= H, Me; R2= H, 2H; R3= H, 2H, Me; X = OH,O2H) has been investigated. It is shown that the reaction is initiated by attack of base (ŌH, Ō2H, ylide) on an allylic proton or [2H]. A mechanism for the reaction is suggested.

7- and 8-membered oxasilacycloalkanes—I : Preparation

Some new α-trimethylsiloxy-ω-methyl(ethoxy)silyl substituted alkanes of the formula (CH 3) 3SiO(CH 2) n-Si(CH 3) x(OC 2H 5) 3-x (x=0, 1, 2; n=5, 6) were synthesized. These compounds are stable and can undergo base catalysed decomposition producing 1-oxa-2-sila-2,2-disubstituted cycloalkanes of the formulae (C 2H 5O) 2-x (CH 3) x Si(CH 2) n O (x = 0, 1, 2; n = 5, 6).

The rearrangements of hydroperoxyindolenines

Examination of a series of substituted 3-)hydroxyperoxy) indolenines favours a mechanism for base catalysed decomposition of the dioxetan rather than Criegee type.

ChemInform Abstract: FUNCTIONALIZED ENAMINES. XXIX. SOLVOLYTIC TRANSFORMATIONS OF 2‐METHYLISOQUINOLIN‐1‐ONE DICHLOROCARBENE ADDUCT. SYNTHESIS OF BENZAZEPINONES

AbstractDas bei der basenkatalysierten Zers. von Chloroform erhaltene Dichlorcarben reagiert mit (I) zum Addukt (II), das mit H2O den Aldehyd (III) ergibt.

Base-catalysed decomposition of nitramide: Brønsted relations and a second reaction pathway

A new spectroscopic technique for measuring the rate of nitramide decomposition revealed a second pathway for this reaction and allowed extension of the Bronsted relation for the first (traditional) pathway into more basic regions where the onset of relatively sharp curvature was detected; these results suggest a mechanism for the first reaction pathway in which proton transfer is not concerted with heavy atom reorganization.

Base-catalysed decomposition of nitramide: kinetic isotope effects

Kinetic hydrogen isotope effects on the decomposition of nitramide catalysed by a series of phosphonate anions and the 2,4,6-trichlorophenoxide ion were found to be small (kH/kDca. 2–3) with no sign of a maximum value of pKa(catalyst conjugate acid)ca. 6, in disagreement with a previously reported claim but consistent with the expected pKa of the reactive form of the substrate.

Synthesis of a 4,5-unsaturated-3-keto sugar (methyl 2-O-benzoyl-4-deoxy-6-O-triphenylmethyl-α-D-glcero-hex-4-enopyranosid-3-ulose)

An approach to the synthesis of the hex-4-enopyranosid-3-ulose 5 has been investigated. The readily available 3-keto derivative 8 is easily debenzylidinated but the resulting diol is benzoylated preferentially at carbon 4 rather than at the primary position. However, tritylation occurs at the primary position and the product is sulfonylated to give the 4-O-methylsulfonyl derivative (11b). lodinolysis of this α-ketosulfonate did not follow an SN2 course giving the desired axial iodide 14b. Instead a course of reductive elimination was observed involving the presumed intermediacy of an enolic hypoiodite. β elimination of methanesulfonic acid from 11b was in fact possible by using diazabicyclononene in benzene-tetrahydrofuran solution. The process undoubtedly involves epimerisation, and the product consists of a mixture of the desired 5 (R = CPh3) and its 2-epimer 22. These enones are prone to base-catalysed decomposition so that although the three steps from the starting ketone 8 to the sulfonate 11b can each be carried out in excellent yield, the final elimination proceeds in 39% yield after isolation.

Reactions of organic peroxides. Part XVI. Amino-peroxides from autoxidation of imines

A number of imines [graphic omitted]N·CHR1 R2(R1= aryl; R2= methyl or aryl), on oxygenation at –15 to –20°(u.v.) or at room temperature (R1 and R2= aryl), gave the corresponding cyclic amino-peroxides [graphic omitted]. Thermal or base-catalysed decomposition of these amino-peroxides provided the corresponding ketones, R1COR2, caprolactam (low yield), and a number of by-products, some of which have been characterised. On the other hand the imines Ph2CH·CH:NR (R = C6H11 or CHPh2) gave rather unstable hydroperoxides, Ph2C(O·OH)·CH:NR, on oxygenation.