Nitrocumyl chloride

A similar mechanism has been proposed for the alkylation of amines by p-nitrocumyl chloride. 

Fig. 6 Passage from the stepwise to the concerted mechanism upon decreasing the driving force. Left potential energy profiles. Right reaction of 4-nitrocumyl chloride with homogeneous donors diamonds 2-nitropropanate ion, squares duroquinone anion radical, circles RNu -. E electrode potential or standard potential of a homogeneous donor.

The mechanism of the thermal 5 rnI reaction, using 4-nitrocumyl chloride and 2-nitropropanate ion as a model has been investigated. The results provided unambiguous evidence that a decrease in driving force is able to change the mechanism of homogeneous reductive cleavage reactions from stepwise to concerted. ... 

Typical one-electron donors, for example, sodium naphthalene, also entrained the reaction of p-nitrocumyl chloride with sodium nitrite (Kornblum et al. 1970). 

If the oxidation is slower than the decomposition, oxygen may affect the nature of reaction products. Thus, treating p-nitrocumyl chloride with sodium malonate ester in a flow of pure dry nitrogen yields a product of C-alkylation (route a in Scheme 5.12) the yield is 90%. Oxygen completely inhibits the C-alkylation, and the reaction gives p-nitrocumyl alcohol in the same yield (route b in Scheme 5.12) (Kornblum et al. 1968). 

When the malonate is absent, oxygen is incapable of converting p-nitrocumyl chloride into alcohol (Kornblum et al. 1968). 

In the presence of oxygen, the reaction in Scheme 5.12 develops in two directions with different rates. The reaction first produces anion-radicals of p-nitrocumyl chloride (the sources of electrons... 

One of the products was the expected C-substituted compound. The other was an unstable species, which decomposed into 4-nitrocumyl alcohol during workup and was ascribed to 0-substitution. Kornblum (1975) had obtained the same products. He considered the C- and 0-substitution as Sj l and S 2 reactions, respectively. Dual reactivity of nucleophiles is well known. Since steric hindrance at the reacting carbon prevents S 2 reaction with 4-nitrocumyl chloride, Costentin et al. (1999) concluded that both the C- and 0-substitution products result from an Sr I reaction. 

Thus, sodium azide and a,p-dinitrocumene do not react unless subjected to the action of light (48-hr control period). In contrast to sodium azide, the lithium salt of 2-nitro-propane reacts with a,p-dinitrocumene in the dark for 3 hr, giving the product of a-substi-tution in 87% yield. When a,p-dinitrocumene (1 mole) is treated with sodium azide (2 moles) in the presence of the lithium salt of 2-nitropropane (only 0.1 mole), the initial a,p-dinitrocumene quantitatively converts into p-nitrocumyl azide for 3 hours. The product is extremely pure, and the reaction requires no UV irradiation (Kornblum et al. 1970) (Scheme 5-3). Typical one-electron donors, e.g., sodium naphthalene, also induced the reaction of p-nitrocumyl chloride with sodium nitrite (Komblum et al. 1970). 

Komblum, N. Stuchal, F. W. New and fatile substitution reactions at tertiary carbon. The reactions of amines with p-nitrocumyl chloride and a,p-dinitrocumene. J. Am. Chem. Soc. 

Nitrocumyl chloride undergoes smooth light-induced substitution by nucleophiles such as phenolate and thiophenolate, benzenesulfinate, azide, cyanide or amines, and the process has been proven to involve a SRN1 mechanism [55,77,78]. 

Dimethyl-2-nitro-3-(4-nitrophenyl)-butane. 4-Nitrocumyl chloride (2.0 g, 10 mmol), the lithium salt of 2-nitropropane (1.9 g, 20 mmol),... 

The nucleophilic photosubstitution reactions of benzylic halides with a nitro group at the ortho- or / ara-position of the aromatic ring such as / -nitrocumyl chloride (26) occur via the S l mechanism. The reactions have been reviewed in References 6-10. The initiation and propagation steps of this photoinduced radical-chain electron transfer process have already been depicted in this review in equations 6 to 9 in Section II. A. Equation 37... 

Kornblum and coworkers31a have determined the quantum yield for the ET substitution reactions of / -nitrocumyl chloride with azide ions (3.5) and quinuclidine (6000). Furthermore, by studying the wavelength dependence of the quantum yields, they have obtained evidence that photochemical initiation proceeds by means of a charge-transfer complex. Similar results have been obtained in the reaction of acetone enolate ion with Phi and PhBr in DMSO, whereas other mechanisms are in competition when Phi reacts with potassium diethyl phosphite3115. 

The reaction between cyanide ions andp-nitrocumyl chloride is the only example reported of an S l reaction involving this anion66b. 

Kornblum and coworkers66b have also reported the reaction betweenp-nitrocumyl chloride and nitrite ion or various amines like piperidine, pyrrolidine, quinuclidine and DABCO. 

Dialkylphosphite ions have been shown to undergo S l reactions with different haloni-tro substrates117. The analogous thiophosphite ions117 react by this mechanism only with p-nitrobenzyl or p-nitrocumyl chlorides, but undergo X-philic reactions with 2-chloro-2-nitropropane. 

A similar mechanism has been proposed for the alkylation of amines by p-nitrocumyl chloride/ Clearly, the tertiary nature of the chloride would make any proposal of an Sn2 mechanism highly suspect. Furthermore, the nitro substituent is essential to the success of these reactions. Cumyl chloride itself gives elimination of HCl to give the olefin on reaction with amines ... 

Addition of p-nitro-a,a-dimethylbenzyl radical to a variety of coordi-natively unsaturated primary, secondary or tertiary amines or ammonia produces the radical zwitterion [10] (Kornblum and Stuchal, 1970). The radical zwitterion will transfer an electron to p-nitrocumyl chloride in the SrnI process. 

Many 5rn1 reactions require external stimulation involving the injection of a catalytic amount of electrons, but thermal 5rn1 reactions are known. In these there is no other source of initiating electrons than the nucleophile, which is usually a poor electron donor. A solution to this conundrum has now been proposed. Initiation follows a mechanism in which electron transfer and bond cleavage are concerted. This conclusion is based on a fuU analysis of a model system involving 4-nitrocumyl chloride as the substrate and the 2-nitropropanoate ion as the nucleophile. All pertinent thermodynamic and kinetic parameters were determined by direct or indirect electrochemical methods. 

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