Benzene reactivity

Low substrate selectivity accompanying high positional selectivity was also found in isopropylation of a range of alkyl and halogenobenzenes by /-propyl bromide or propene in nitromethane, tetramethylene sulphone, sulphur dioxide, or carbon disulphide, as indicated by the relative rates in Table 86. The toluene benzene reactivity ratio was measured under a wide range of conditions, and varied with /-propyl bromide (at 25 °C) from 1.41 (aluminium chloride-sulphur... 

The reliability of this work has also been questioned by Brown and Nelson339, who could not get any reaction at all with benzene under the conditions quoted by Szmant and Dudek382. If the benzene value is in error it could account for the low selectivities that were observed. By using the competition technique with a deficiency of paraformaldehyde (but an excess of hydrogen chloride) they obtained a toluene benzene reactivity ratio of 112 and partial rate factors of / Me = 117, /mMc = 4.37, /pM = 430. 

CAS 26913-06-4. (CH2CH2NH) . A synthetic polymer that is a highly viscous, hygroscopic liquid when anhydrous completely miscible with water and lower alcohols insoluble in benzene. Reactive toward cellulose. Combustible. 

Toluene-benzene reactivity ratios under a number of Friedel-Crafts conditions are recorded in Table 9.9. As would be expected on the basis of the low substrate selectivity, position selectivity is also modest. The amount of ortho product is often comparable to the para product. Steric effects play a major role in determining the o p ratio in Friedel-Crafts alkylations. The amount of ortho substitution of toluene... 

The resonance between phenol oxygen and the benzene ring also affects benzene reactivity. The extra electron density in the ring makes it susceptible to electrophilic attack by even rather weak electrophiles Reactions with formaldehyde and CO2 in the presence of base arc examples. 

Figure 17.3. Robinson showed how benzene reactivity could be understood in terms of mobile electrons moving around the benzene ring. He used arrows to show electron movements.

Table 9.10. Toluene-Benzene Reactivity Ratios in Friedel-Crafts Alkylation Reactions... 

The similarity of benzene reactivity with that of an alkene ends, however, at the carbocation stage, prior to nucleophilic attack. As we saw in Chapter 14, benzenes closed shell of six TT electrons give it special stability. 

Toluene-benzene reactivity ratios in Friedel-Crafts alkylation reactions... 

What Is the Benzylic Position, and How Does It Contribute to Benzene Reactivity ... 

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