Neutral Methanol Research Articles

Cumulene photochemistry: photoaddition of neutral methanol to phenylallenes

Ultraviolet irradiation of tetra-, tri-, or diphenylallene in methanol leads to allylic methyl ethers. A mechanism is proposed with intermediacy of a strongly polarized planar allene excited state, initially protonated at C 2.

The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study

AbstractAb initio molecular orbital calculations with moderately large polarization basis sets and including valence‐electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH3OH2]+. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH5O]+ potential surface. There is no evidence for a tightly‐bound complex, [HOCH2]+…︁H2, analogous to the preferred structure [CH3]+…︁H2 of [CH5]+. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol−1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol−1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol−1 but with a reverse activation barrier of 149 kJ mol−1). The results offer a possible explanation as to why production of [CH2OH]+ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol−1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol−1).

Cleavages of 1-methyl-2-trimethylsilylbenzimidazole and 2-trimethylsilylbenzothiazole in methanol and related media

First-order rate constants k at 25 °C have been determined for the cleavage of 1-methyl-2-trimethylsilylbenzimidazole (I) and 2-trimethylsilylbenzothiazole (II) in MeOH, alone or containing NaOMe, and in 5 : 2 v/v MeOH–H2O containing HClO4. Compound (I) is cleaved rapidly by neutral methanol (103k 51 s–1)(and also by H2O, 103k 110 s–1 or EtOH, 103k 3.0 s–1); very small amounts of NaOMe do not affect the rate (which thus refers to a spontaneous process), but larger amounts induce a base-catalysed process (102k8 63 l mol–1 s–1). The data for the neutral cleavage of (I), including a rate isotope effect, r.i.e. [given by the ratio k(MeOH)/k(MeOD)], of 3.3, can be interpreted either in terms of the cyclic mechanism involving a solvent molecule previously proposed for cleavage of 2-trimethylsilylpyridine or one in which MeO– attacks the protonated substrate. In base cleavage (I) gives an r.i.e. of 1.1, and this is interpreted in terms of proton transfer to the N of the NC bond synchronous with breaking of the C–SiMe3 bond, but (II) gives an r.i.e. of 0.46, suggesting that there is little if any such electrophilic assistance. The low product isotope effects (the product ratio RH/RD on cleavage in 1 : 1 MeOH–MeOD) of 1.2–1.3 for neutral cleavage of (I) and the base cleavages of (I) and (II) are attributed to the fact that the isotopic composition of the products is determined in a step involving transfer of hydrogen to a localized carbanion. Addition of acid greatly raises the rate of cleavage of (II) in 5 : 2 MeOH–H2O, but reduces it for (I), for which the rate levels off at a value thought to refer to the fully protonated species. The acid-catalysed processes may involve attack of a solvent molecule at silicon in the protonated species.

Interaction of bovine carbonic anhydrase with (neutral) aniline, phenol, and methanol.

We have investigated the interaction of bovine carbonic anhydrase with neutral aniline, phenol, and methanol molecules. The measurements are of optical spectra and solvent water and methanol proton magnetic relaxation rates of solutions of Co2+-substituted enzyme. We recently proposed a model [Koenig, S. H., Brown, R. D., & Jacob, G. S. (1980) Proceedings of the Symposium on Biophysics and Physiology of Carbon Dioxide, Springer-Verlag, West Berlin and Heidelberg], based on the interaction of enzyme with monovalent anions, that accounts for the pH dependences observed for a wide variety of phenomena, including the apparent pKa for enzymatic activity. We now extend the model to include the observed effects of neutral molecules. Aniline and phenol, though isoelectronic, shift the observed pKa values in opposite directions, and both appear to bind at the aromatic binding site to which sulfonamide inhibitors and aromatic esters are known to bind. The resulting binary complexes behave as altered enzymes, with different values of the pKa for activity, but otherwise are similar to the native enzyme. In terms of our model, aniline and phenol alter the relative affinities of water and anions for the same coordination position of the metal ion at the active site. The effect is opposite in sign for the two nolecules becuase of the differing proton affinities of the NH2 and OH moieties of the phenol ring in each case. By extension, our results indicate that data from experiments using aromatic buffers such as imidazole and lutidine should be analyzed with some care; effects previously attributed to buffer molecules to the aromatic binding site in the active region of the enzyme. The interaction of methanol with carbonic anhydrase is quite different, and very weak. Methanol does displace water at the metal, but to first order there is little, if any, preferential binding of methanol compared to water. Observations by others that alcohols inhibit esterase activity with inhibition constants on the order of 1 M are not attributable to binding of alcohol to enzyme but rather, in our view, result from the increased solubility of aromatic ester substrates in the alcohol-modified solvent.

On the photooxygenation and autoxidation of dipyrrylmethenes and dipyrrylmethanes

AbstractThe dye‐sensitized photooxygenations of 4,4′‐diethyl‐3,5,3′5′‐tetramethyldipyrrylmethene and 4,4 ‐diethyl‐3,5,3′5‐tetramethyldipyrrylmethane have been investigated in neutral, basic and acidic methanol solution. Several photoproducts are common to the photooxygenation of both substrates. The dipyrrylmethene was detected as an intermediate in the photooxygenation of the dipyrrylmethane; however, it was determined not to be an important precursor to monopyrrole products. Autoxidations of the two dipyrrole compounds were also investigated and were found to be slower than the corresponding photooxygenation. Autoxidation and photooxygenation were both found to be faster in basic than in acidic methanol with the dipyrrylmethane faster than with the dipyrrylmethene in the same solvent.

ChemInform Abstract: IPSO NITRATION. XX. NITRATION OF 5‐TERT‐BUTYL‐1,2,3‐TRIMETHYLBENZENE IN ACETIC ANHYDRIDE. FORMATION AND REAROMATIZATION OF ADDUCTS

AbstractNitrierung der Titelverbindung (I) in Acetanhydrid liefert die Verbindungen (IIa), (IIb), (IVa), (Va) und (III).

Ipso nitration. XX. Nitration of 5-tert-butyl-1,2,3-trimethylbenzene in acetic anhydride. Formation and rearomatization of adducts

Nitration of 5-tert-butyl-1,2,3-trimethylbenzene in acetic anhydride gives both diastereomers of the adduct 1-tert-butyl-3,4,5-trimethyl-4-nitrocyclohexa-2,5-dienyl acetate and one diastereomer of 1-tert-buty]-3,4,5-trimethyl-4-nitrocyclohexa-2,5-dienol, in 91% yield, together with 5-tert-butyl-1,2,3-trimethyl-4-nitrobenzene. Solvolysis of the dienyl acetate in acidified aqueous acetone and acidified methanol affords the diastereomers of the dienols and the dienyl methyl ethers, respectively. The dienyl methyl ethers are also formed from the dienyl acetate in neutral methanol and again on reaction with methanolic sodium methoxide. The dienols isomerize (epimerize) in acidified aqueous acetone. Reaction of the dienyl methyl ethers in aqueous methanol, or prolonged reaction in methanol, results in the formation of methyl-1,2,3-trimethylphenyl ether. Similar cleavage of the tert-butyl group is the main reaction on solvolysis of the dienyl acetate in aqueous acetic acid. Under more acidic conditions the dienyl acetate gives 5-tert-butyl-2,3-dimethylbenzyl nitrite and lesser amounts of 5-tert-butyl-2,3-dimethylphenylnitromethane and 5-tert-butyl-2,3-dimethylbenzyl acetate. In trifluoromethanesulfonic and fluorosulfonic acids 5-tert-butyl-1,2,3-trimethyl-4-nitrobenzene is the major product.

Less polar forms and derivatives of 18 hydroxy-corticosterone

The formation of various compounds upon reaction of 18 hydroxycorticosterone with neutral and acid-added alcohols as well as with acidic aqueous solutions is described. The time course of their formation in such media has been studied. Some of these compounds have been isolated and tentatively identified by paper chromatography employing double isotope techniques and by mass spectrometry. The more polar form has a C-20 hemiketalic structure; the single less polar form obtained upon storage in neutral methanol would be the methylketal at C-20 but the less polar fraction having the same mobility in the Chromatographie system employed, obtained upon reaction with acidic aqueous solutions, seems to be formed by two different dehydration products.

The chemistry and biogenesis of the S-containing metabolites of vinyl chloride in rats

In order to determine whether vinyl chloride yields chloroethylene oxide in vivo, the biogenesis of the various urinary S-containing metabolites in rats has been investigated. N-Acetyl- S-(2-hydroxyethyl)cysteine is a major vinyl chloride metabolite in rats, but according to the method of protective esterification that is used, so either N-acetyl- S-(2-chloroethyl)cysteine or N-acetyl- S-(2-hydroxyethyl)cysteine may be isolated from the body fluids. N-Acetyl- S-vinylcysteine is a second related metabolite. These S-containing vinyl chloride metabolites are not mutagenic in S. typhimurium. Neutral methanol methylates N-acetyl- S-(2-hydroxyethyl)cysteine. N-Acetyl- S-(2-methoxyethyl)cysteine plus N-acetyl- S-vinylcysteine degrade to give the volatile S-(2-methoxyethyl)(prop-1 or 2-enyl)sulphide. Administration of several vinyl chloride metabolites and closely related compounds to rats shows that chloroacetaldehyde and S-(carboxymethyl)cysteine, but not chloroacetic acid, lie on a pathway or pathways connecting vinyl chloride with thiodiglycollic acid. The fact (a) that chloroacetaldehyde affords both thiodiglycollic acid and N-acetyl- S-(2-hydroxyethyl)cysteine in the animal and (b) that S-(carboxymethyl)cysteine has been identified amongst the hydrolytic products from an hepatic extract prepared from vinyl chloride-treated animals is consistent with the formation of chloroacetaldehyde, and with the reaction of chloroethylene oxide or chloroacetaldehyde with glutathione in the presence of a glutathione S-epoxide transferase to give the identified S-containing metabolites.

Flavonoid Analysis of Hybridization in Rhododendron Section Pentanthera (Ericaceae)

Flavonoid Analysis of Hybridization in Rhododendron Section Pentanthera (Ericaceae)

Mechanism of the photochemical substitution of 6-membered ring monoazaaromatic compounds by methanol in neutral and HCl acidified medium

6-Membered ring monoazaaromatic compounds such as pyridine, quinoline, 4-methylquinoline, isoquinoline and 9-phenylacridine are converted to the corresponding semiquinone radicals when irradiated in methanol acidified with HCl, ether or neutral methanol. In a neutral medium the hydrogen photoabstraction occurs from an nπ * excited state by a monophotonic process, but in methanol acidified with HCl, the photoreaction corresponds to a biphotonic process. In this case the photoreaction involves an electron transfer from methanol to a protonated upper excited triplet state of the solute (Scheme 2, path 2).

Pyridoxamine analogs. Absorption spectra and metal chelate formation in methonol.

The absorption spectra of salicylamine (ο-hydroxybenzylamine) (I), thiosalicylamine (ο-mercaptobenzylamine) (II), and 3-hydroxy-4-aminomethylpyridine (III), have been measured at various concentrations of added acid or alkali in methanol solution. Assignments of the absorption bands to the various molecular species are made. I existed as a nonpolar species, whereas II did as a dipolar species with a dissociated thiol group, in neutral methanol solutions. This was supported by the pKa values (I ; 9.2, 10.5 : II ; 4.7, 9.5) calculated from potentiometric titration curves in aqueous solutions. Both polar and nonpolar species were present in a neutral methanol solution of III. The Al [III], Cd [II], Ni [II] and Zn [II] chelates of II were fairly stable, whereas those of I were not formed appreciably, in methanol. III formed Al [III], Cd [II], Cu [II], Ni [II], and Zn [II] chelates, spectra of which were quite similar to those of metal chelates of pyridoxamine. Spectral change of a solution containing II and Cu [II] ion shows II formed Cu [II] chelate and, then, was converted to benzisothiazol. In the presence of Zn [II] ion, II and sodium pyruvate formed Zn [II] chelate of ketimine Schiff base, which underwent tautomerization to that of aldimine Schiff base very slowly. Possible correlation is noted between pKa's of the phenolic group of pyridoxamine and its analogs and their abilities to form metal chelates and to catalyze the nonenzymatic transamination.

ChemInform Abstract: AN ANOMALOUS PRODUCT IN THE PHOTOLYSIS OF BENZOPHENONE IN ACIDIFIED METHANOL

AbstractDie Belichtung von Benzophenon (I) in Methanol in Gegenwart von konz. Schwefelsäure ergibt Benzoesäuremethylester (II), das Pinakol (III) und das Diphenyläthandiol (IV).

Photochemistry of 2,4-Cyclooctadienone. II In Neutral and Acidic Methanol

Irradiation of 2,4-cyclooctadienone (1) in neutral dry methanol resulted in the formation of 3-methoxy-4-cyclooctenone (18%) and two head-to-head 2 + 2 dimers (combined yield 64%). A similar irradiation in acidic methanol (0.001 N HCl) caused a dramatic change in the products formed. A new compound, the dimethyl ketal of trans, cis-2,4-cyclooctadienone was formed in 67% yield along with the two dimers (<10%). A mechanism is proposed whereby the photochemically derived trans, cis-2,4-cyclooctadienone reacts in thermal processes to give the products described. Low temperature trapping experiments which support this hypothesis are discussed.

An anomalous product in the photolysis of benzophenone in acidified methanol

Benzophenone when irradiated in a 2% solution of hydrochloric acid in methanol, gave methyl benzoate as the only isolable product, whereas in neutral methanol, benzopinacol and 1,1-diphenylethane-1,2-diol were formed.

Permeation Dynamics and Osmoregulation in Aphelenchus Avenae

Specific rate constants for the diffusion controlled permeation of Aphelenchus avenae by a wide variety of organic substances and the equilibrium constants for the process have been measured. In general, hydrophobic, nonpolar, organic soluble structures permeate the quickest and have the greatest affinity for the nematodes. In contrast, salts, hydrophilic, and polar substances are the slowest permeators and have the lowest affinity for the animals. The nematicide 1,3-dichloropropene in the fastest permeator (kin = 1.3 min-1, kout = .094 min-1) and glucose is one of the slowest (kin = 1.3 × 10-4 min-1, kout = 5 × 10-3 min-1). The small neutral polar molecules, water, acetone, and methanol are an exception to these findings. The rate in and out of these substances is unusually rapid. The results suggest a different path of permeation for those substrates. The water permeation rates are not affected over a wide range of osmotic pressure but the animals do decrease in size. The rate of shrinkage is slow at an osmotic pressure of 10 atm but approaches the rate of water permeation at 26 atmospheres. The results establish water movement as the dominant primary event in osmoregulation.

Base-catalysed solvolysis of N-(trialkylsilyl)anilines

Rates of solvolysis have been measured for the compounds PhNHSiMe 3, PhNHSiEt 3, m-ClC 6H 4NHSiEt 3, PhNMeSiEt 3, and PhNEtSiEt 3 in a mixture of methanol (5 vol) and aqueous potassium hydroxide (2 vol), and for most of these compounds in mixtures of dimethyl sulphoxide (6 vol) and aqueous alkali (1 vol). All the compounds react rapidly with neutral aqueous methanol. For the secondary compounds PhNHSiMe 3 and PhNHSiEt 3, the rates fall when a little alkali is added and the oxonium ion catalysed reaction is suppressed, but then rise as the alkali concentration is increased further, and a base-catalysed reaction takes over. Base catalysis is, however, very much less effective than acid catalysis. There is also a significant “spontaneous” reaction involving catalysis by neutral molecules. For the tertiary compounds PhNMeSiEt 3 and PhNEtSiEt 3, base catalysis is not significant in MeOH/H 2O but does contribute in DMSO/H 2O. There is a very large difference in reactivity between PhNHSiMe 3 and PhNHSiEt 3 in the base-catalysed reaction in MeOH/H 2O, the former being ca. 2.5 x 10 4 times more reactive; this is attributed to unusually severe steric hindrance. Mechanisms are suggested for the neutral, base-catalysed, and spontaneous reactions.

Mechanism of the formation of semiquinone radicals by ultra-violet irradiation of six-membered aromatic aza-compounds in neutral methanol, and of radical cations by ultra-violet irradiation of six-membered aromatic diaza-compounds in methanol acidified with hydrochloric acid

9-Phenylacridine and quinoxaline react with methanol but do not directly abstract a hydrogen radical from the solvent; in methanol–HCl, pyrazine, quinoxaline, and phenazine give radical cations.

Biochemical aspects of the visual process: XIV. The binding site of retinaldehyde in rhodopsin studied with model aldimines

In view of diverging opinions on the binding site of 11- cis retinaldehyde in the visual pigment rhodopsin, the effects of neutral and acidic methanol and borohydride-methanol on cattle rhodopsin and on synthetic retinylidene imines were compared with the following results. 1. 1. Extraction of rhodopsin with neutral methanol yielded 70–90% of the chromophore as retinylidene phosphatidylethanolamine. However, addition of phosphatidylethanolamine to a solution of a N-ϵ-retinylidene lysine derivative in neutral methanol resulted in substantial transiminization to retinylidene phosphatidylethanolamine. 2. 2. Acidification of the methanol reduced the amount of retinylidene phosphatidylethanolamine extracted from rhodopsin to virtually zero at 10 −2 m HCl. This phenomenon was neither caused by insolubility of the aldimine, nor was it paralleled by a decrease of lipid-soluble phosphorus extractable into the acidified methanol. In a model system consisting of a N-ϵ-retinylidene lysine derivative and a 25-fold molar excess of phosphatidylethanolamine in methanol, transiminization was observed at HCl concentrations of 5.10 −4 m or less, but not at 10 −3 m HCl or higher. 3. 3. Addition of sodium borohydride to rhodopsin, followed by methanol, gave no indication at all for retinyl phosphatidylethanolamine, whereas retinylidene phosphatidylethanolamine was quantitatively reduced under the same conditions, even in the presence of excess of another free amine. Upon alkaline hydrolysis of the methanol-insoluble residue, left after reduction, the chromophore was located as a compound absorbing around 330 nm, which was tentatively identified as retinyl lysine. The experiments with rhodopsin, interpreted in the light of the model experiments, virtually exclude the possibility that 11- cis retinylidene phosphatidylethanolamine could be the chromophore in native rhodopsin.

The Reactions of Photogenerated Solvated Electrons in Methanolic Solutions of Potassium Iodide

Abstract Hydrogen formation from UV-irradiated potassium iodide solutions was studied using CH3OH and CH3OD as the solvents and nitrous oxide and acids as the solvated-electron scavengers. The maximum quantum yield of the solvated electron in CH3OH was found to be 0.6 both in nitrous oxide and in acid solutions. It was concluded that the solvated electron produces hydrogen in pure methanol through Reaction (1), e−solv→H+CH3O−, with a quantum yield of 0.35 at 25°. The rate constant of this reaction is 5.4×105sec−1, corresponding to a half-life of 1.3 μsec. From the results obtained with acid solutions, it was also concluded that nitrous oxide reacts with a solvated electron to produce one molecule of nitrogen in neutral methanol.