Chemistry & Biochemistry Theses and Dissertations
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Item The Photochemistry of Amides and Phthalimides(1977) Bowen, Michael William; Mazzocchi, Paul H.; Organic Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md); ILLiad # 1481769N-Alkyl amides undergo photodecomposition much slower than their ketone, ester, and aldehyde analogs . The Norrish Type II process in amides is also less important than in these other classes of compounds due to electronic and geometric effects. Type II products account for less than 10% of the decomposed amides in all cases and usually less than 5%. A 2% solution of amide in dioxane, when irradiated through quartz with light >200 nm, did not decompose in the Type II fashion to yield N-alkyl acetamides, alkenes, and unsubstituted amides. The preferred reaction mode was the Norrish Type I process where the O=C+N bond or the O=C+C bond was cleaved to yield either an acyl radical and amine radical or an acyl radical and alkyl radical. These photochemically unstable radicals, once produced, rapidly underwent secondary reactions to yield smaller molecules. These molecules were detected, underwent further reactions (polymerization; photoreduction), or interacted with the solvent . The dimers of dioxane and cyclohexane, created via hydrogen abstraction, were the main products of amide photodecomposition in these solvents. Small aldehydes and alkenes produced as intermediates, underwent inefficient photoreductions with solvent to afford alkyl dioxanes and cyclohexanes and the two diastereomers of ( 2-p-dioxyl ) ethanol as other major products. The alcohols were also produced by photoreduction of acetaldehyde and hexanal as well as by direct photodecomposition of dioxane . Tertiary amides reacted faster than secondary amides. The Type I reaction was accelerated by electronic (inductive) factors. The Type II reaction was also more efficient due to geometric and electronic factors. The Type I amine product, dihexylamine, was observed as an intermediate in the photodecomposition of N, N-dihexylhexanoamide . Unsymmetrical anilide imides photodecomposed in dioxane to yield a wide variety of products. The Photo-Fries decomposition mode was most favored where acyl groups migrated to positions ortho and para to the amine substituent. For example, N-acetyl-butyranilide decomposed to yield o- and p-acetoaniline, o - and p-butyraniline , o- and p-acetobutyranilide, and o- and p-butyracetanilide. Very little Type II decomposition was observed, that is, N-acetyl-butyranilide yielding N, N -diacetylaniline or o- and p-acetoacetanilide. N-Alkylphthalimides were the sole group of amides or imides reported in the literature to undergo efficient Y-hydrogen abstraction. These compounds underwent initial Y-hydrogen abstraction to yield a 1,4-biradical followed by ring closure to form an azacyclobutanol intermediate. The intermediate then underwent retrotransannular ring opening to yield various 3,4-benzo-6,7-dihydro(1H)azepine-2,5-diones. Dihydrophthalimide alkenes were minor products in acetonitrile which arose after the initial y-hydrogen abstraction via subsequent δ-hydrogen transfer. Quantum yield determination as well as mechanistic investigation was conducted . The quantum yields varied from 0.023 to 0.003. Photolysis of an optically active phthalimide with an asymmetric Y-position to yield starting material of the same activity proved that the initial hydrogen abstraction was irreversible. A Type I cleavage to yield phthalic anhydride on treatment with silica gel and heat was important when they Y-position was tertiary. A quenching study of these N-alkylphthalimides with piperylene showed acceleration of starting material disappearance but decrease in product formation. An additional reaction process was interfering with the azepinedione formation. Liquid chromatography showed formation of several highly alkylated products which could not be isolated in pure form. N-Methylphthalimide, which could not ring expand, was irradiated with various alkenes to produce analogous N-methylazepinediones. The mechanism involved a 2 + 2 cyclo-addition of the double bond to the C-N bond to yield a dipolar azacyclobutanc intermediate. The intermediate with a retrotransannular ring opening yielded the observed 3, 4- benzo-6,7-dihydro-1-methylazepine-2,5-diones. These reactions prove that the C-N bond in phthalimide is of a substantial double bond character.Item The Effect of Changes in Structure of the Reactants on the Rate of Enamine Formation(1964) Marchese, James Salvatore; Pratt, Ernest F.; Chemistry & Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)It has been found that the rate of formation of a wide variety of enamines can be accurately determined by observing the rate at which the by-product water collects in a Dean-Stark trap. On the basis of the results observed upon varing the reactant ratio, the catalyst concentration and the temperature, 0.125 mole of carbonyl compound, 0.375 mole of amine and .001 mole of p-toluenesulfonic acid dissolved in sufficient benzene to give a total volume of 500 ml. were employed in the standard procedure. The solution of reactants was heated under reflux in an apparatus fitted with a water trap and frequent readings of time and water volume were taken until the reaction was complete. Nearly quantitative (98 to 100%) yields of water were ordinarily obtained and 85 to 100% yields of enamine were usually isolated. As the structure of the carbonyl component was varied an extremely wide range of reaction rates was encountered. The relative reactivity of many of these compounds had not been determined preciously. It was found that the rate decreased markedly among cyclic ketones as the ring was expanded from five to six to seven members and also when the methyl group of methylcylohexanones were shifted from the four to the three to the two position, Steric effects appear to be responsible for these rate differences. Somewhat unexpectedly ∝-tetralone did not react while β-tetralone reacted smoothly. Although the literature contains very little information on the formation of enamines of diketones a number of these were converted to the mono-enamines very smoothly. The rate decreased in the sequence, 1, 3-cyclohexanedione, dimedone, acetylacetone, benzoylacetone and 2-acetylcyclopentanone. Some evidence that ketones having planar structures reacted faster than those with non-planar structures was found, but no obvious correlation between degree of enolization and rate of reaction was observed. The reaction of acetophenones was much improved when the reaction temperature was changed from 82° to 112° by using toluene as a solvent. As the electron attracting ability of the para substitute was inreased in the order, CH3, H, Cl and N02 the rate consistently increased. Phenylacetone reacted smoothly under the standard conditions, but heptanone-2 gave only a 27% yield of water in five days . The importance of steric factors is emphasized by the fact that cyclohexanone gave a 98% yield of water in two hours. Typical aliphatic aldehydes reacted so rapidly that in order to increase the accuracy of t;he rate measurements 0.000125 mole of catalyst was used in place of the standard 0.001 mole. The order of decreasing rate was phenylacetaldehyde, It is apparent that the rate decreasing effect of chain branching at the alpha position diminishes when the branches are joined into a ring. The results for phenylacetaldehyde and phenylacetone indicated that aldehydes react over one thousand times as fast as ketones. The rate of formation of enamines from cyclohexanone and a variety of amines was also determined under the standard conditions. Shifting a methyl group on the piperidine ring from the four to the three to the two position greatly decreased the rate and pyrrolidine reacted faster than both piperidine the and hexamethylene imine. Morpholine and especially N methylpiperazine reacted much faster than piperidine while n-butylmethylamine reacted most slowly of all the amines mentioned. In only a few special cases was integral order kinetics obtained. The results can, however, be quite well correlated with a straightforward mechanism if it is assumed that both the step in which the amine adds to the carbonyl group and the step in which this addition product is dehydrated ordinarily affect the overall rate.Item Micro-scale Chemical Effects of Low Temperature Weathering of DSDP Basaltic Glasses(1979) Ailin-Pyzik, Iris Blanche; Sommer, Sheldon E.; Chemistry & Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Unaltered deep-sea basaltic g lasses are believed to be the best record of initial magma composition , and as such are important in the study of petrogenesis. However , these glasses are altered by their long contact with seawater, becoming hydrated and undergoing chemical exchange. This chemical exchange affects the composition of seawater and plays a role in the chemical equilibrium of t he oceans. A study of the trace metal and major element alteration of glasses from Deep Sea Drilling Project Site 396B has been conducted, using a selected area x - ray fluorescence technique (developed for this study) for the trace metal analyses, and the electron rnicroprobe for the major elements. The samples included sections of pillow basalt rinds, hyaloclastite s, and a few crystalline sections. The glasses were found to release a bout o ne- half the original Si and Al, two- thirds of the Mg and Na , and over 90% of the Ca originally present, during alteration to palagonite. Fe and Ti were found to be immobile, and K was increased 40-fold by concentration from seawater. For the trace metals, over one-quarter of the Zn, Cu and Ni were released, 40% of the Mn, and over 10% of the Cr. These changes apply only to the conversion of fresh glass (sideromelane ) to palagonite (smectite), and do not include the effects of authigenic phillipsite and calcite reprecipitated locally. Differences between the effects of low temperature weathering on the crystalline basalts and the glasses appear to be primarily a function of the susceptibility of the primary mineral phases to attack, with the glass, being the least stable phase, being the most altered.