Sulphoxides dehydration

Hydroxyalkyl sulphoxides 515 can be dehydrated either by treatment with phosphoric acid (equation 315) or by the alkylation with Mel in the presence of an excess of sodium hydride611 (equation 316). For other dehydration reactions see References 475 and 505 (Section IV.A.2.d). For elimination of amines see References 164 and 529 (Section IV.A.2.e). 

Dimethyl sulphoxide brings about the dehydration and oxidation reactions in some alcohols. 

Nitrosolysis of camphor ethyl acetal with ethanolic ethyl nitrite in sulphur dioxide yields the orthoester oxime (205) which is rapidly dehydrated by excess acetal to the orthoester nitrile which then reacts with sulphur dioxide to form the ester nitrile and diethyl sulphite.Further papers in this section include the full paper on ozonolysis of silyl ethers (Vol. 5, p. 33), another synthesis of camphor-enol trimethylsilyl ether (cf. Vol. 6, p. 41)/°° the conversion of camphor oxime with Grignard reagents into the corresponding imine with no aziridine formation/° the preparation of (206) by treating bornylene with trichloroacetyl isocyanate/ the oxidation of thiocam-phor to the 5-oxide and alkylation in the presence of thallium(i) ethoxide to a/S-unsaturated sulphoxides/ and the free-radical C-3 alkylation of camphor with alkenes. " ... 

Two further reactions might be included here, since they involve modification at both carbon and sulphur. In the first reaction, dehydration of the sulphoxides 388 (R = Me or aryl R = H, Me, ethenyl or Ph) to the diethyl [(l-alkylthio)alk-l-enyl]phosphonates 389 is said to result following the action of trimethylsilyl trifluoromethanesulphonate The second reaction constitutes a new and improved synthesis of an ester of (mercap-tomethyl)phosphonic acid, and consists in the treatment of methyl (diisopropylphosphi-noyl)dithioformate with NaBH4. ... 

Two reviews have appeared which are concerned particularly with the role of solid catalysts in dehydration reactions . Kieboom and van Bekkum have reported details of the dehydration of 2-aryl-3-methyl-2-butanols by sulphuric acid and by dimethyl sulphoxide. Surprisingly, for both reactions, the kinetic product is the thermodynamically less stable 2-aryl-3-methyl-l-butene, which subsequently isomerises to 2-aryl-3-methyl-2-butene. Steric interactions were proposed to account for the initial formation of the less stable alkene in the reaction of the carbonium ion. Significant proportions of the Hoffmann... 

Oximes as well as amides (p. 249) are converted into nitriles by some silicon derivatives. Hexamethylcyclotrisilazane (8) when heated at 210° for 6 hr with benzaldoxime gives benzonitrile in 72% yield [35]. Carbodiimides in pyridine have a similar action on amides [48]. By replacing pyridine by triethylamine and either ether or carbon tetrachloride, and addition of acetyl or phenacetyl chloride, aldoximes may be converted to nitriles at low temperature [62] examples are PhCN (86.6%), PhCH = CH.CN, (81.4%) and 2-cyanofuran (82.6%). A car-bodi-imide, trifluoroacetic acid and dimethyl sulphoxide (DMSO) mixture has been shown to dehydrate 4-bromobenzaldoxime [63]. 

Side-chain chlorination to 2,3-dichloromethylpyridine with JV-chloro-succinimide followed by ring-closure with sodium sulphide, oxidation to the sulphoxide with phenyliodonium chloride, and dehydration on AI2O3 according to the method of Cava gave (540). Curiously, attempts to prepare the benzo-analogue (541) by the same method were unsuccessful. However, the transient existence of (541) could be demonstrated by trapping with A -phenylmaleimide. ... 

Since dimethyl sulphoxide has also a reasonably high dielectric constant, the ionized compounds are considerably dissociated. Due to its high donor properties dimethyl sulphoxide dissolves various classes of chemical compounds. Many organic compounds including polymers are soluble. Numerous reactions, such as elimination, dehydration, isomerization, substitution, condensation, addition and redox-reactions may be carried out in dimethyl sulphoxide solutions with great easei. ... 

Dimethyl sulphoxide is a useful reaction medium in organometallic synthesis. For example potassium hydroxide acts both as a protonating and dehydrating agent in dimethyl sulphoxide to enable the formation of ferrocene from hydrated ferrous chloride and cyclopentadiene . ... 

New phosphorus-based deoxygenating agents include P2I4, which reduces epoxides to alkenes, besides dehydrating aldoximes to nitriles, and Ph3Pl2 and (Me2N)3P-l2-NaI which reduce sulphoxides to sulphides. ... 

Few dehydration methods work well for allyl alcohols, and even fewer are regiospecific. The sulphoxide in Scheme 19 is derived from an allyl alcohol by... 

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