Oxygen to sulfur

This simple valence-bond rationale, involving a resonance hybrid of forms 1 and 2, appears to explain many of the physical data available for sulfoxide complexes. It appears that S-bonding does not involve such a major internal rearrangement of the molecule as one may initially expect and is almost certainly a result of the increased orbital diffuseness on passing from oxygen to sulfur. Thus with typical hard acids (see ref. 437), orbital overlap will be most favorable with the less diffuse donor orbital of oxygen. In the case of typical soft metals, this overlap is less favorable due to the orbital diffuseness of the soft acid, and so coordination via sulfur occurs, where the orbital diffuseness of the donor and acceptor are more evenly matched. 

An O-labelling investigation of the oxygen to sulfur transposition in the base-catalysed rearrangement of o-benzoyl-A-(diphenylphosphinothioyl)hydroxylamine (200) to (201) has been undertaken. The labelling results are outlined in Scheme 70 although further evidence is required to substantiate the mechanism... 

The 4-oxo-group of the 4-oxo-4//-pyrido[l,2-a]pyrimidines was transformed to a thioxo group by diphosphorus pentasulfide in pyridine,2 49 71 Under similar conditions the oxygen to sulfur exchange could not be achieved... 

Carbon dioxide is lost on thermolysis of 4-ethoxycarbonyl-2-phenyl-A2-l,3,4-oxadiazo-line-5-thione. Migration of the ethyl group from oxygen to sulfur leads to the product, 5-ethylthio-2-phenyl-l,3,4-oxadiazole (78IJC(B)146). 

The BF3 and BCI3 complexes of diethyl ether are less stable than those of dimethyl ether, and the same order of stability is observed for the complexes of diethyl and dimethyl sulfides. As expected, steric interaction decreases as the distance between the metal and ligand atom is increased. Thus, it decreases when the metal atom is changed from boron to aluminum, or when the ligand atom is changed from oxygen to sulfur. 

The pATa of isoselenazoles was measured by spectrophotometric methods. The values were compared to isothiazoles and isoxazoles (Table 8). The basicity increases from oxygen to sulfur to selenium, being enhanced by the dimethyl groups <88H(27)243i>. 

In the double-catalysis plant a major portion of the sulfur trioxide is removed from the gas in an intermediate absorption tower after the second stage of conversion. The balance of the gas, which is returned to the converter for the final two stages of conversion, is a very weak sulfur dioxide gas with a high oxygen-to-sulfur dioxide ratio. The equilibrium conditions for this gas leaving the converter are very close to 100% conversion of the total sulfur dioxide entering the converter. In steady state operation, which is not possible with copper converter gas, over 99.8% conversion of sulfur dioxide to sulfur trioxide is expected in double-catalysis plants. 

There are times during the operating cycle of the copper converter when the oxygen-to-sulfur dioxide ratio is lower than is desirable. During these periods dilution air must be mixed with the gas entering the drying tower of the contact section of the plant to increase its oxygen content. 

Rearrangement of O-Thiocarbamates to S-Thiocarbamates (Newman-Kwart Rearrangement) Another mechanistically related reaction to the Chapman rearrangement is that named after Newman [32] and Kwart [33]. This particular variant involves the 1,3-migration of an aryl group from oxygen to sulfur in a thiocarbamate (Scheme 18.11), and the reaction has recently been reviewed [34]. 

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