Bromoethane reactions

As was the case with bromoethane, reactions with bromohexane also gave poor results, both in the one-step procedure and in the two-step procedure, reduction of the aromatic ketone becoming the main reaction. 

Into the reaction flask is added 912g crystalline guaiacol and 1500g regular 48% HBr which is then slowly heated to reflux. The tepid water condenser is there to allow the bro-momethane that is formed to leave the reaction flask but is still cold enough to keep the other reactants in the reaction flask. The noxious bro-moethane condenses in the cold water condenser and drips into the chilled methanol in the collection flask. This will keep this bromoethane trapped so that the chemist will not die... 

This method is merely an application of the Grignard reaction but is a lot less troublesome because it uses really common chemicals. This method can be done as it was done in the reference where a phenylbutene was made using a bromopropane ( bromo-propane and bromoethane are cheap to purchase or can be made... 

Vlayl fluoride [75-02-5] (VF) (fluoroethene) is a colorless gas at ambient conditions. It was first prepared by reaction of l,l-difluoro-2-bromoethane [359-07-9] with ziac (1). Most approaches to vinyl fluoride synthesis have employed reactions of acetylene [74-86-2] with hydrogen fluoride (HF) either directly (2—5) or utilizing catalysts (3,6—10). Other routes have iavolved ethylene [74-85-1] and HF (11), pyrolysis of 1,1-difluoroethane [624-72-6] (12,13) and fluorochloroethanes (14—18), reaction of 1,1-difluoroethane with acetylene (19,20), and halogen exchange of vinyl chloride [75-01-4] with HF (21—23). Physical properties of vinyl fluoride are given ia Table 1. 

Let s look at a typical polar process—the addition reaction of an alkene, such as ethylene, with hydrogen bromide. When ethylene is treated with HBr at room temperature, bromoethane is produced. Overall, the reaction can be formulated as... 

Because XL.q is relatively large, the reaction proceeds as written and greater than 99.999 99% of the ethylene is converted into bromoethane. For practical purposes, an equilibrium constant greater than about 103 means that the amount of reactant left over will be barely detectable (less than 0.1%). 

We call the carbocation, which exists only transiently during the course of the multistep reaction, a reaction intermediate. As soon as the intermediate is formed in the first step by reaction of ethylene with H+, it reacts further with Br in a second step to give the final product, bromoethane. This second step has its own activation energy (AG ), its own transition state, and its own energy change (AG°). We can picture the second transition state as an activated complex between the electrophilic carbocation intermediate and the nucleophilic bromide anion, in which Br- donates a pair of electrons to the positively charged carbon atom as the new C-Br bond starts to form. 

Thus, the acetoacetic ester synthesis of 2-pentanone must involve reaction of bromoethane. 

Let us consider one other reaction of ethanol. If ethanol is heated with aqueous HBr, we find that a volatile compound is formed. This compound is only slightly soluble in water and it contains bromine its molecular formula is found by analysis and molecular weight determination to be C2HsBr (ethyl bromide, or bromoethane). With the aid of the bonding rules, we can see that there is only one possible structure for this compound. This result is verified by the fact that only one isomer of C2H6Br has ever been discovered. 

Convince yourself of this fact by writing an equation using the structural formulas 1 and 3. In contrast, bromoethane can be obtained from structure 2 only through a complicated rearrangement. Two carbon-oxygen and one carbon-hydrogen bond would have to be broken. Experience shows that such complicated reshufflings of atoms rarely occur. Therefore, the reaction between ethanol and hydrobromic acid, HBr, to form bromoethane provides more evidence that ethanol has structure 1. 

Synthesis of bromoethane (ethane + HBr) and of dibutyltin dibromide (bromobutane + Sn). Other halogenation reactions such as bromina-tion of p-xylene to tetrabromoxylenes is of importance as an efficient fire extinguishing agent for plastics. 

Hydroboration of alkenes in non-ethereal solvent has been reported using diborane generated in situ from a quaternary ammonium borohydride and bromoethane (see Section 11.5). Almost quantitative yields of the alcohols are reported [e.g. 1 ]. As an alternative to the haloalkane, trimethylsilyl chloride has also been used in conjunction with the ammonium borohydride [2]. Reduction of the alkene to the alkane also occurs as a side reaction (<20%) and diphenylethyne is converted into 1,2-diphenylethanol (70%), via the intermediate /ra 5-stilbene. 

Rajagopal and Burris (1999) studied the degradation reaction of ethylene dibromide in water with zero-valent iron. Ethylene dibromide degraded rapidly following pseudo-first order kinetics. The observed end products were ethylene and bromide ions and were probably formed via a P-elimination pathway. Bromoethane and vinyl bromide were not observed as possible intermediate products. 

To illustrate the Spj2 mechanism, consider the reaction between the primary haloalkane bromoethane and the nucleophilic hydroxide ion. A study of the kinetics of the reaction reveals that it has the following rate equation rate = /cfCHjCH BrllOH ]. 

The nucleophilic hydroxide ion attacks the C atom in the bromoethane from the side opposite to the C-Br bond and begins to form a covalent bond with it. At the same time, the C-Br bond begins to break. A transition state is then reached in which the new 0-C bond is partially formed and the C-Br bond is partially broken. The reaction is completed by the formation of the full 0-C bond and the complete break-up of the C-Br bond. 

A Steady-State and Time-Resolved Fluorescence Study of Quenching Reactions of Anthracene and 1,2-Benzanthracene by Carbon Tetrabromide and Bromoethane in Supercritical Carbon Dioxide (Zhang et al., 1997)... 

The rate constant for the second-order reaction between bromoethane and hydroxide ions in water, C2H5Br(aq) + OH (aq) C2H5OH(aq) + Br (aq), was measured at several temperatures, with the following results ... 

A facile route to isothiochromans involves the base-catalyzed reaction of a benzyl dibromide with an a-thiocarbonyl compound. The method has been extended to the synthesis of an anthraceno[2,3-f]thiopyran, a heterocyclic analogue of an anthracyclinone (Equation 169) <1994S363>. In like manner, alkylation of the 2-aryl-1-bromoethane 491 by thiourea and subsequent liberation of the thiol function creates an isothiochroman precursor. An intramolecular Michael addition to the cr, )-unsaturated ester side chain yields the 1-substituted heterocycle (Scheme 179) <1992JOC1727>. 

Caution The intermediate, 1 -phenylthio-2-bromoethane, produced in the first step of this one pot reaction sequence is a strong alkylating agent, and some bromine escapes from the reaction vessel. Therefore the reaction should be run in a properly operating ventilation hood, and care must be exercised to avoid exposure to these substances. 

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