Ethyl halides

Secondary alkyl halides react by a similar mechanism involving attack on benzene by a secondary carbocation Methyl and ethyl halides do not form carbocations when treated with aluminum chloride but do alkylate benzene under Friedel-Crafts conditions The aluminum chloride complexes of methyl and ethyl halides contain highly polarized carbon-halogen bonds and these complexes are the electrophilic species that react with benzene... 

SELECTIVE HALOGEN-LITHIUM EXCHANGE REACTIONS OF 2- 2 -HAL0PHENYL)ETHYL HALIDES ... 

The haloethanes all have similar rotational barriers of 3.2-3.7 kcal/mol. The increase in the barrier height relative to ethane is probably due to a van der Waals rqjulsive efiect. The heavier halogens have larger van der Waals radii, but this is ofiset by the longer bond lengths, so that the net efiect is a relatively constant rotational barrier for each of the ethyl halides. 

There is another useiiil way of depicting the ideas embodied in the variable transition state theory of elimination reactions. This is to construct a three-dimensional potential energy diagram. Suppose that we consider the case of an ethyl halide. The two stepwise reaction paths both require the formation of high-energy intermediates. The El mechanism requires formation of a carbocation whereas the Elcb mechanism proceeds via a caibanion intermediate. 

A nonconventional synthesis of the known inhalation anaesthetic, 2-bromo-2 chloro-l,l,l-trifluoroethane (Halothane), based on the reaction of ethyl 1,2 di bromo-1,2-dicliloroethyl ether with anhydrous hydrogen fluoride and sulfur tetrafluoride, has been patented The reaction presumably involves cleavage of the ether linkage, followed by fluorination of the intermediate bromochloroacetyl halide with sulfur tetrafluoride, ethyl halides are the by-products [2] (equation 2)... 

We have mentioned earlier that when ethanol reacts with hydrogen bromide, ethyl bromide is formed. Similar treatment of ethanol with hydrogen chloride or hydrogen iodide gives us the corresponding ethyl halides ... 

We say that the hydroxyl group has been displaced, and the halogen atom substituted for it. You can see that the group CH3CH2— has remained intact in all of these reactions. Indeed, this group has appeared in most of our discussion so far, sometimes attached to oxygen (as in ethanol and sodium ethoxide), sometimes attached to other atoms (as in the ethyl halides). You will recall that earlier we became acquainted... 

A. Nucleophilic Reactions.—(/) Attack on Saturated Carbon. The Arbusov reaction has been used to prepare organosilicon-substituted phosphonates (1) and phosphorylated ethers (2a) and sulphides (2b). Bromo- and chloro-derivatives of the cyclic phosphite (3) do not react with ethyl halides... 

Koplitz and co-workers have studied the photolysis of C2H5 via the A2A (3s) state by using 248-nm photolysis radiation and hot ethyl radicals generated from photolysis of ethyl halides.125,126 Chen and co-workers have investigated the photodissociation of jet-cooled ethyl (produced by flash pyrolysis of ethyl iodide and n-propylnitrite) in the region of 245-264 nm... 

Dry hydrogen halide was passed into the ester. The ethyl halide was trapped at — 78°, and the weight of it served to indicate the progress of dealkylation. Dealkylation being completed, volatile matter was removed from the residue at low pressure. Crude acids were thus obtained in absence of water. Similar results to those obtained at 100° were obtained at 25°, but of course longer reaction time was required. 

C2H 50.CH3-CH3.0C2H6 mw 118.17, color less liq with si ethereal odor, sp gr 0.8417 at 20/20°, fr p -74°, bp 121.4°, fl p 95°F, vapor pressure 9.4mm at 20° partially miscible with w. It can be prepd by reacting the Na alcoholateof an ethyleneglycol ether with ethyl halide or by reacting diethyl sulfate with the ethyleneglycol monoethyl ether (Refs... 

Studies by Nakane et al. also support the two-step mechanism when alkylation is carried out with alkyl halides under substantially nonionizing conditions. It was further shown that in nonpolar organic solvents carbocations rather than the polarized complexes participate directly in the formation of the first n complex. BF3—H20 catalyzes ethylation,130 isopropylation,131 and benzylation132 through the corresponding carbocations. Accordingly, ethylbenzene equally labeled in both a and p positions was obtained when [2-14C]-ethyl halides were reacted in hexane solution in the presence of boron trifluoride, BF3—H20, or aluminum... 

Cross, P. C., and J. H. van Vleck Molecular vibrations of three particle systems with special applications to the ethyl halides and ethyl alcohol. J. chem. Phys. 1, 350—356 (1933). 

Scheme4.40. Alkylations with 2-(acylamino)ethyl halides and alcohols [157-159],...

Other problematic electrophiles are 2-(acylamino)ethyl halides and related compounds. Although numerous successful nucleophilic substitutions with such substrates have been described in the literature, occasionally a side reaction becomes dominant. If the leaving group is hard or if the reaction conditions chosen are conducive to the formation of carbocations, intramolecular O-alkylation of the electrophile will lead to the formation of oxazolines (Scheme 4.40). This cyclization can sometimes be avoided by choosing a softer leaving group. 

Calculations on ethyl halide reactions include that on the SN2 reaction between ethyl chloride and cyanide ion in DMSO.112 The calculated free energy of activation at the CCSD(T)/6-31+G(2df,2p) level on the B3LYP/6-31G(d)-optimized structure was within 1.5 kcalmol-1 of the experimental value. 

Mg2Pb alloy is also reactive with alkyl halides higher than ethyl halides whereas sodium-lead alloy is not, except in the presence of water and pyridine 167,274) xhis hydrous system was used briefly in the 1920 s for the commercial production of tetraethyllead 67). 

The reaction of alkyl halides with sodium-lead alloy is quite sensitive to many reaction factors. The monosodium-lead alloy reacts at a fast rate only with ethyl chloride. The presence of other ethyl halides or methyl halides in the ethyl chloride inhibits the reaction severely, and the presence of as little as 0.0025% acetylene in the ethyl chloride retards the reaction strongly 284>. 

---