No description available.

No description available.

Efficient syntheses for appropriately derivatized methyl 8R,9(R and S), 11R-trihydroxy-12-oxododeca-5Z-enoates (53, 59) via their respective 5,6-anhydro-3-deoxy-1,2-0-isopropylidene-(alpha)-D-hexofuranoses (18 and 38) are described. These aldehydes were subsequently converted to the corresponding methyl 8(R and S), 9(R and S), 11R-trihydroxy-eicosa-5Z,12E,14Z-trienoates (64, 72, 82, 91). Model studies towards the synthesis of 8R,11R,15(R and S)-trihydroxy-9S,12-oxyeicosa-5Z,13E-dienoic acids (1) were carried out.

Thesis (Ph. D.)--Columbia University, 1937. / Vita. Bibliography: p. [38-39].

This report describes a kinetic study of the thermal decomposition of methyl disulfide. The study was made as a contribution to the chemistry of organic sulfur compounds. The homogeneous decomposition was studied by the static method in an all-glass apparatus. It was followed by observation of the accompanying pressure changes and by analysis of the reaction mixture at various stages of the reaction. Several new analytical methods were developed for this analysis. The experimental conditions were varied by varying the temperature of the decomposition, the pressure of the reactant, and the surface to volume ratio of the reaction vessel, and by adding various substances to the reacting system. The experimental results show that the reaction is composite: (1) Initially a fraction of the reactant disulfide adsorbs on the surface of the pyrex reaction vessel at a rate which agrees with the theoretical rate for a collision mechanism. (2) There follows an induction period during which the disulfide does not decompose. (3) The first decomposition is into methyl mercap-tan and a non-volatile product believed to be a thiofor-maldehyde polymer. The suggested overall reactions are: CH₃-S-S-CH₃ → CH₃SH + CH₂=S n CH₂=S → (-CH₂-S-)n (4) A later, competing, process produces hydrogen sulfide, ethylene, free sulfur and polysulfides. It is possible that the carbon disulfide formed is produced by this reaction, and it is probable that the thioaldehyde polymer is decomposed. The overall unbalanced reactions may be written: CH₃SSCH₃ + ((CH₂S)n?) → H₂S + C₂H₄ + S + (CS₂?) + (?) CH₃-S-S-CH₃ + Sₓ → CH₃-Sₓ -CH₃ (5) Secondary reactions continue long after the disulphide has been used up. The major process appears to be the degradation of the postulated polythioformaldehyde to hydrogen sulfide and possibly to carbon disulfide and ethylene. Degradation of the polysulfides appears to occur also, and there may well be further secondary reactions. The nature of the various component processes have been discussed in some detail, and lines of further research have been suggested. The structure of disulfides and polysulfides and the bonding of organic sulfur compounds have been discussed. / Science, Faculty of / Chemistry, Department of / Graduate

The [Cp'M(NO)₂]BF₄ (M = Cr, Mo or W; Cp' = Cp or Cp*; except CpW) cations effect the condensation of methylpropiolate and 2-methyl-2-butene within their coordination spheres. The isolated product ratios of the reaction vary with the formation of the six-membered ring [Cp'M(NO)₂-C=C(H)C(Me)(H)C(Me)₂OC(=OCH₃)]BF₄ complexes being favoured over the five-membered ring [Cp'M(NO)₂- C=C(H)C(Me)(C(H)(Me)₂)OC(=OCH₃)]BF₄ complexes. Furthermore, the isolated product ratios vary from metal to metal with the percentage of six-membered ring product increasing from Cr < Mo < W. The connectivity extant in the molecular structures of the cationic complexes was determined by single crystal X-ray crystallographic analysis of a representative example of this class, [Cp*Cr(NO)₂-C=C(H)C(Me)(H)C(Me)₂OC(=OCH₃)]BF₄. These cationic lactone complexes may be demethylated by reacting their THF solutions with Nal to afford the neutral lactone complexes, Cp'M(NO)₂-C=C(H)C(Me)(H)C(Me)₂OC(=O) and Cp'M(NO)₂-C=C(H)C(Me)(C(H)(Me)₂)OC(=O). 2-Methyl-2-pentene and methyl propiolate are condensed in the presence of [Cp*Mo(NO)₂]BF₄ to generate the six-membered ring complex as the only isolable product. The condensation of methylpropiolate and diphenylacetylene or 1-phenyl-1-propyne by [Cp*Mo(NO)₂]BF₄ results in an unprecedented formation of the cationic α-pyrone complexes [Cp*Mo(NO)₂-C=C(H)C(R)=C(Ph)OC(=OCH₃)]BF₄ (R = CH₃ or Ph). These complexes may be demethylated to produce the neutral a-pyrone complexes, Cp*Mo(NO)₂-C==C(H)C(R)==C(Ph)OC(=0) (R = CH₃ or Ph). Only one regioisomer is formed with the regiochemistry of the 1-phenyl-1-propyne complex being confirmed by a single crystal X-ray crystallographic analysis of the neutral complex, Cp*Mo(NO)₂-C=C(H)C(CH₃)=C(Ph)OC(=O). / Science, Faculty of / Chemistry, Department of / Graduate

Bacteria (Arthrobacter sp.), isolated from lodgepole pine (Pinus contortus), are capable of utilizing methyl dehydroabietate as the sole source of carbon. Degradation products of methyl dehydroabietate have been obtained by manually extracting the cell-free supernatant solution of a liquid growth medium with methylene chloride. Gas chromatography (G. L. C.) was used for separation of the neutral products. The acid products were converted to their methyl esters diazomethane and then separated by gas chromatography. Structures have been proposed for two G. L. C. fractions (V, II) on the basis of infrared (I.R.) and mass spectral (M. S.) data. The molecular weight of V is 328, corresponding to the introduction of one oxygen atom into methyl dehydroabietate, (M. W. 314) and loss of two protons. Infrared peaks at 5.73µ and 5.77µ. , and the absence of a large P-l mass spectral peak (P-1 is due, to loss of the aldehydic hydrogen) indicate that the material is a keto- ester. A comparison of the fragmentation pattern of V and the fragmentation pattern of methyl dehydroabietate indicates that the ketone carbonyl group is in ring A of methyl dehydroabietate and is β to the ester carbonyl group. The molecular weight of II is 260. Present in its infrared spectrum are peaks associated with a non-conjugated methyl ester (5.73µC=O; 8. 30µ, 8. 39µ, 8. 54µ, C-O) and the aromatic ring (6. 21µ, 6. 67µ, and 6.89µ) with isopropyl substitution (7. 30µ, 7.37µ). Significant mass spectral peaks at (1) 233 (P-27), (2) 201 (P-59), (3)200 (P-60), (4) 159 (P-101) and (5) 129 (P-131) are consistent with structure II.

CH3Br and CH3Cl (methyl halides) are the most abundant natural vectors of bromine and chlorine into the stratosphere and play an important role in stratospheric ozone destruction. The current knowledge of their respective natural sources is incomplete leading to large uncertainties in their global budgets. Beside the issue of quantification, characterisation of possible sources is needed to assist modelling of future environmental change impacts on these sources and hence the stratosphere. This study describes measurements conducted at two temperate salt marsh and three temperate forest sites in Scotland, and one tropical rainforest site in Malaysian Borneo to quantify and characterise natural methyl halide producing processes in these respective ecosystems. Measurements were conducted with static enclosure techniques, and methyl halide fluxes were calculated from the concentration difference between blank/background and afterenclosure samples. Methyl halide concentrations were determined via oxygen-doped GCECD with a custom-built pre-concentration unit. External factors such as photosyntheticallyactive radiation (PAR), total solar radiation, air temperature, soil temperature, internal chamber temperature and soil moisture were recorded in parallel to the enclosures to determine possible dependencies. Salt marsh studies were carried out at Heckie’s Hole in East Lothian, and Hollands Farmin East Dumfriesshire for 2 years. The study subjects were salt marsh plants that were enclosed during daylight hours in transparent enclosures for 10min each at 2–4 week intervals throughout the year. Parallel to this monitoring programme, systematic manipulation experiments and diurnal studies were carried out to learn more about the possible influence of potential drivers such as sunlight and temperature. Mean annual net fluxes ( standard deviation (sd)) were 300 44 ngm-2 h-1 for CH3Br and 660 270 ngm-2 h-1 for CH3Cl, with fluxes of both gases following a diurnal as well as an annual cycle, being lowest during winter nights and highest during summer days. A possible link between variations of daytime fluxes over the course of a year and changes in temperature was found. CH3Cl and CH3Br fluxes were positively correlated to each other and average fluxes of CH3Cl were linked to dry mass of certain species such as Puccinellia maritima, Aster tripolium, Juncus gerardi and Plantago maritima as found at the different measurement locations. No link between methyl halide fluxes and total halogen content or halogen concentration of the enclosed vegetation was found. Work in temperate forests was carried out for over one year at Fir Links, a mixed beech/ sycamore forest in East Lothian, and on one occasion each in Griffin Forest, a sitka spruce plantation in Perthshire, and finally the Hermitage of Braid, a mixed woodland park in Edinburgh. The study subject was leaf and needle litter which was enclosed in opaque 12 L containers for 10min–24h. During enclosure, internal chamber temperature was recorded, and leaf/needle litter water content was determined after enclosure. Combined average CH3Br and CH3Cl fluxes from temperate forest litter were 4.3 10-3 ngg-1 h-1 and 0.91 ngg-1 h-1, respectively. Average fluxes measured from leaf and needle litter were comparable in magnitude and CH3Br and CH3Cl were positively correlated. However no correlation of methyl halide fluxes to either temperature or litter water content was observed. Work at Danum Valley inMalaysian Borneo focused on flux measurements from both trees and leaf litter in a tropical dipterocarp forest. Fluxes from tropical trees were measured with transparent branch chambers at 20min enclosure times whilst methyl halide fluxes from leaf litter were measured with opaque 12 L containers at 24h enclosure times. Mean CH3Br and CH3Cl fluxes from branch enclosures were 0.53 ngg-1 h-1 and 27 ngg-1 h-1, respectively, and CH3Br and CH3Cl fluxes from tropical leaf litter were 1.4 10-3 ngg-1 h-1 and 2.3 ngg-1 h-1 respectively. Again fluxes of CH3Br and CH3Cl were positively correlated but no direct environmental driver for flux variations was found. The magnitude of methyl halide fluxes was species specific with individuals of the genus Shorea generally producing large amounts of methyl halide. Tropical rainforests were confirmed to be potentially the largest single natural source of CH3Cl. Global estimates were derived from extrapolating measured fluxes from the respective global land cover areas. These estimates suggest that the ecosystems examined in this study could account for over 1/3 of global CH3Cl production and up to 13%of global CH3Br production in nature. The ratio of CH3Br to CH3Cl emissions for these ecosystems is likely to be dependent on the abundance of bromine in the plant material with higher bromine content boosting CH3Br production and suppressing CH3Cl production. For this reason salt marshes are only a very minor source of CH3Cl.

No description available.

Methyl bromide (CH3Br) and methyl chloride (CH3Cl) are two halocarbons that are unique in that they play a significant role in stratospheric ozone destruction, and are mainly produced by natural systems. The current average tropospheric mixing ratios are 7.9 pptv CH3Br and 550 pptv CH3Cl (WMO, 2007). Although CH3Br and CH3Cl are present in such low concentrations, their atmospheric life times are sufficiently long that they can be transported to the stratosphere via the tropical tropopause at the equator. This process takes approximately six months.