Reactions at an Oxygen Atom

Hydroxyalkyltellurophenes were acetylated and oxidized to the corresponding carbonyl derivatives . 

2-(l-Hydroxyethyl)-tellurophenes reacted with acetic anhydride in pyridine at room temperature to form acetyloxy derivatives . The esters were saponified in aqueous ethanol s. 

4-Bis[hydroxymethyl]-2,5-diphenyltellurophene was oxidized to the 3,4-diformyl derivative upon heating with selenium dioxide at 200° under a nitrogen atmosphere . 

With activated manganese dioxide as the oxidizing agent, the yield was only 1 %. Attempted oxidations with silver carbonate, chromium trioxide, and lead tetraacetate were unsuccessful. 2-(Methoxyphenyl)tellurophenes were converted to 2-(hydroxyphenyl)tellurophenes upon treatment with sodium ethanethiolate or boron tribromide.  

2-(4-Hydroxyphenyl)-telliirophene 0.92 g (11 mmol) of sodium ethanethiolate are dissolved in 9 ml of dimethylformamide (DMF), the solution is stirred under nitrogen, and 0.4 g (1.4 mmol) of 2-(4 -meth-ox) phenyl)-tellurophene in 9 ml of DMF are added. The mixture is heated at 80° for 144 h, cooled, diluted with water, and extracted with diethyl ether. The aqueous phase is acidified with 10% hydrochloric acid, the acidified aqueous phase is extracted with diethyl ether, and the organic extracts are combined, dried with anhydrous sodium sulfate, filtered, and concentrated under vacuum. The residue is chromatographed on silica gel with light petroleum ether (b.p. 40-60°)/diethyl ether (4/1, v/v) as the mobile phase. The product is recrystaUized from ligroin/chloroform (1/1, v/v) yield 0.1 g (26%) m.p. 160 . 

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The formation of quaternary salts by attack at an oxygen atom is only achievable in certain special cases. Most of the attempts to effect reactions of this type with N-alkyl-a-oxo derivatives have failed. Until recently it might have been assumed that 2-alkoxy-quaternary salts were unobtainable, the usual product from reactions with the alkoxy derivatives being the N-alkyl-oxo compounds (see Section IV,C). Recently, however, Meerwein and his co-workers found that triethyloxonium borofluoride and a number of N-methyl-a-oxo... 

Corrections for Improper HF Asymptotic Behaviour.—There are two techniques which may be used to obtain results at what is essentially the Hartree-Fock limit over the complete range of some dissociative co-ordinate in those cases where the single determinants] approximation goes to the incorrect asymptotic limit. These techniques are (i) to describe the system in terms of a linear combination of some minimal number of determinantal wavefunctions (as opposed to just one) 137 and (ii) to employ a single determinantal wavefunction to describe the system but to allow different spatial orbitals for electrons of different spins - the so-called unrestricted Hartree-Fock method. Both methods have been used to determine the potential surfaces for the reaction of an oxygen atom in its 3P and 1Z> states with a hydrogen molecule,138 and we illustrate them through a discussion of this work. 

Another example of nucleophilic attack of anilines at an oxygen atom has been reported by Buxton and coworkers134. The oxidation of 4-substituted /V,/V-dimethylanilines by dimethyldioxirane, 13, in acetone showed a similar qualitative trend as those for the reactions at the Mel and benzoyl peroxide reactions with a reactivity decrease in the order X = MeO > H > Cl N02. These trends suggest that the oxidation of DMAs by 13 is electrophilic. The px value of —0.89 shows similarity to the values in the reactions of DMAs with Mel (Menschutkin reaction) which has a px value of —3.30 at 35 °C in 90% aqueous acetone. While in the latter reactions the TS is thought to have developed almost a full positive charge, the reactions with 13 have much less charge development partially due to steric crowding in the TS (Scheme 17). 

We have seen that an enolate of a ketone is a nucleophile that can displace a leaving group from a primary alkyl halide. Although the enolate has two reactive sites, we have already learned that reaction of an electrophile with an enolate occurs at the a-carbon atom to give a substituted keto product called the C-alkylated product. The alternate reaction at the oxygen atom to give an O-alkylated product occurs much less commonly. 

AN OVERVIEW OF PHENOL toms of the aromatic ring. For reactions at the oxygen atom, phenols act as nucleophiles and react... 

In Europe, interest has centered particularly on polyhydroxybutyrate, which can be made into films for packaging as well as into molded items. The polymer degrades within 4 weeks in landfills, both by ester hydrolysis and by an ElcB elimination reaction of the oxygen atom p to the carbonyl group. The use of polyhydroxybutyrate is limited at present by its cost—about four times that of polypropylene. 

The alkali chlorates melt before decomposition [844], The catalytic properties of Co304 in promoting [865] the solid phase decomposition of NaC103 are attributed to the ability of the oxide to donate an electron to an oxygen atom, temporarily accepted at its surface from a CIO ion, prior to molecular oxygen formation and desorption. The progressive increase in E during reaction (from 120 to 200 kJ mole-1) is associated with systematic deactivation of the surface. 

Nitrogen oxides also play a significant role in regulating the chemistry of the stratosphere. In the stratosphere, ozone is formed by the same reaction as in the troposphere, the reaction of O2 with an oxygen atom. However, since the concentration of O atoms in the stratosphere is much higher (O is produced from photolysis of O2 at wavelengths less than 242 nm), the concentration of O3 in the stratosphere is much higher. 

The carbonyl group also possesses electrophilic properties at the carbon atom and nucleophilic properties at the oxygen atom. Nucleophilic attack of the carbonyl group is favored if this is attached to an aromatic ring (inductive effect) and there is also a methoxy or phenolic OH group present in the 4-position. Changing a neutral reaction medium by proton addition has the same effect. 

For a better understanding of the effect of changing concentrations on the rate of a chemical reaction, it helps to visualize the reaction at the molecular level. In this one-step bimolecular reaction, a collision between molecules that are in the proper orientation leads to the transfer of an oxygen atom from O3 to NO. As with the formation of N2 O4, the rate of this bimolecular reaction is proportional to the number of collisions between O3 and NO. The more such collisions there are, the faster the reaction occurs. 

At elevated temperature, NO2 reacts with CO to produce CO2 and NO CO + NO2 CO2 + NO In one possible mechanism for this reaction, products form directly in a one-step bimolecular collision that transfers an oxygen atom from NO2 to CO ... 

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