Sulfur compared

Make a molecular model of dimethyl sulfide How does its bond angle at sulfur compare with the C—O—C bond angle in dimethyl ether"d... 

Properties. The properties of naphtha, gas od, and H-od products from an H-coal operation are given in Table 7. These analyses are for Hquids produced from the syncmde operating mode. Whereas these Hquids are very low in sulfur compared with typical petroleum fractions, they are high in oxygen and nitrogen levels. No residual od products (bp > 540° C) are formed. 

The torsional barrier of the amino group in thioamides is generally ca. 2 kcal/ mol higher than in the corresponding amides (26), and this trend is also found in the enamino thioketones (17,23 Table 2). The increased conjugative interaction in the thioamides is reflected in the Ct—C2 barriers, and the larger size of sulfur compared to oxygen affects the EIZ population ratio. 

From the above discussion it is evident that alkylation of 1,2,3-benzotriazin-4-one results almost entirely in substitution at Nj and/or Nj, and that alkylation on oxygen is at most a minor reaction. Alkylation of l,2,3-benzotriazine-4(3//)-thione (39, R = H), on the other hand, leads to predominant or exclusive substitution on sulfur, presumably as a result of the greater nucleophilicity of sulfur compared to oxygen. This difference in reactivity between the oxygen (10, R = H) and sulfur (39, R = H) compounds has been elegantly demonstrated by Murray and Vaughan. Treatment of the sodium salt of 10, R = H, with phenacyl bromide gives the Nj-substituted derivative 127, which, on... 

With the advent of large sour gas sulfur production in Western Canada that began in the early 1960 s, Canada became a large net exporter of sulfur. In 1979, Canada produced about 6.0 million long tons of sour gas sulfur, compared with local demand of about... 

On the supply side, sulfur production is now controlled more by the demand for energy through the desulfurization of fuels than by the demand for sulfur per se, and this tendency is increasing. In 1965 involuntary byproduct recovered sulfur amounted to less than 20% of total elemental sulfur production in the United States and Canada, but by 1980 over 60% of all elemental sulfur resulted from refinery and natural gas processing operations. Many future hydrocarbon energy sources (coal, deep gas, heavy oil, shale, etc.) contain considerably more sulfur compared with conventional hydrocarbon fuels, and thus their exploitation will add to the ever increasing supply of by-product sulfur. 

Type A systems seem to behave as two separate aromatic rings, since there is a good deal of evidence for a lack of interaction between the two parts. Compounds with a central double bond (e.g., 482 and 483) are more stable than, for example, 484, at least when one of the heteroatoms (X and Y) is sulfur [compare 282b (Section IV,A,1) and 89 (Section V,B)]. Peri-interactions between free lone pairs can destabilize a system. 

O-protected cyclic or acyclic carbon frameworks. The choice of acetals or ethers as derivatives allows a systematic manipulation of diols and polyols. Kinetic control and a lesser affinity for protonation on sulfur compared with oxygen allows the transformation of cyclic hemiacetals into acyclic dialkyl dithioacetals. Acetal, ether, and dithioacetal derivatives are some of the pivotal intermediates needed to explore various applications of carbohydrates in synthesis. 

The acidity difference of hydrogen atoms adjacent to divalent sulfur compared to oxygen stems from the greater polarizability of sulfur and the longer C-S-bond length d-orbitals are not involved. In most cases treatment of dithianes with w-BuLi at temperatures of -30 °C is sufficient for the preparation of the lithio-derivatives. With pKA values of approximately 30, lithiated dithianes can react with aldehydes or ketones, epoxides and acid derivatives, but also with alkyl halides without competing elimination reactions. 

This carbon-sulfur comparability extends only to sp and sp2 hybridized carbon, meaning only to unsaturated systems. The following series of examples illustrates this. 

For 1,3,4-thiadiazole, the lower electron supply from the sulfur compared to the oxygen equivalent accounts for the ortho meta para rate ratio in the phenyl ring of 1 3 2 in the 2-phenyl derivative (7.56) no substitution took place at the 5-position (53JPJ701). 

Crude shale oil is an important potential source of transportation fuels when properly refined. However, although it is low in sulfur compared with mid-East crudes, it is much higher in nitrogen than typical petroleum crudes. The shale oil used in this study contains 2.2 wt % nitrogen typical petroleum crudes contain less than 0.3% nitrogen. 

We have already stressed that acetals are far more susceptible to hydrolysis than thioacetals and Scheme 2.62 attests to the assertion.133-135 The high acid stability of 55-acetals compared with 0,0-acetals may be attributed to the lower Bronsted basicity of sulfur compared with oxygen and the barrier to formation of a thionium ion with its bond. The large number of methods that... 

The most utilized Umpolung strategy is based on formyl and acyl anion equivalents derived from 2-lithio-l,3-dithiane species. These are readily generated from 1,3-dithianes (thioacetals) because the hydrogens at C(2) are relatively acidic (p f 31). In this connection it should be noted that thiols (EtSH, pi 11) are stronger acids compared to alcohols (EtOH, 16). Also, the lower ionization potential and the greater polarizability of the valence electrons of sulfur compared to oxygen make the divalent sulfur compounds more nucleophilic in Sj,2 reactions. The polarizability factor may also be responsible for the stabilization of carbanions a to sulfur. ... 

The well-controlled attack of ozone on the sulfur molecule can best be explained by the assumption that a terminal oxygen of the ozone molecule executes an electrophilic attack on the sulfur, forming a new bond with the sulfur. [Compare with Meinwald s work (4) for the analogy in the attack of ozone on the double bond.] Thereupon, the second and third atoms of the ozone are liberated as molecular oxygen. This theory explains the fact that only one oxygen from each ozone molecule is added to the sulfur. If one assumes an attack of the apex oxygen of the ozone molecule, it is difficult to understand why only one of the oxygen atoms stays associated with the sulfur. 

How similar are the two classes of proteinases How do the structural differences affect the activity of CP Are the relative rates for acylation and deacylation similar in CP and SP How does the more polarizable and less electronegative sulfur compare to oxygen along the formation of the TI, and during hydrolysis of a thioester vs. an ester ... 

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