Dehydrohalogenation of Alkyl Halides
Dehydrohalogenation of alkyl halides is a chemical reaction in which a hydrogen halide is removed from an alkyl halide, resulting in the formation of an alkene. This process typically involves the use of a strong base to abstract the acidic hydrogen from the alkyl halide, leading to the formation of a carbon-carbon double bond. Dehydrohalogenation is an important method for synthesizing alkenes in organic chemistry.
4 Key excerpts on "Dehydrohalogenation of Alkyl Halides"
eBook - ePub- James G. Speight(Author)
- 2019(Publication Date)
- Gulf Professional Publishing(Publisher)
...The result is loss of the double bond (or alkene structure), and the formation of the alkane structure. For example, unsaturated hydrocarbons (alkene derivatives and alkyne derivatives) readily react with halogens by addition reactions with halogens: halogen atoms (X) are added across the double (C C) or triple (C C) bond. As an example: CH 3 CH CHCH 3 + X 2 → CH 3 CHXCHXCH 3 In this equation, X 2 is the halogen. The most commonly encountered halogens in the halogenated hydrocarbon products are fluorine and chlorine, but sometimes bromine or iodine occur, or combinations of any of these. In the hydrohalogenation reaction, an alkene derivative reacts with a molecule that contains one hydrogen and one halogen—hydrogen chloride (HCl) and hydrogen bromide (HBr) are common hydrohalogen derivatives that are used in this reaction type. In hydrohalogenation, the hydrohalogen is a polar molecule, unlike the nonpolar molecules observed in the halogenation and hydrogenation reactions. In the case of the hydrohalogen, the end of the molecule containing hydrogen is partially positive, while the end of the molecule containing the halogen is partially negative. Thus, when the negatively charged electron from the alkene double bond attacks the hydrohalogen, it will preferentially attack the hydrogen side of the molecule, since the electron will be attracted to the partial positive charge. The halogen will then form the negatively charged anion observed in the intermediate structure and attach second during the addition reaction. The final product is a haloalkane...
eBook - ePub- Graham Patrick(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...SECTION L — ALKYL HALIDES L1 Preparation and physical properties of alkyl halides Key Notes Preparation Alkenes are converted to alkyl halides by reaction with hydrogen halides. Treatment with halogens results in dihaloalkanes. Tertiary alcohols can be converted to alkyl halides on treatment with hydrogen halides, whereas primary and secondary alcohols are best converted by using thionyl chloride or phosphorus tribromide. Structure Alkyl halides consist of an alkyl group linked to a halogen. The carbon linked to the halogen is sp 3 hybridized and tetrahedral. The carbon–halogen bond length increases and the bond strength decreases as the halogen increases in size. Bonding The C–halogen bond (C–X) is a polar σ bond where the halogen is slightly negative and the carbon is slightly positive. Intermolecular bonding is by weak van der Waals interactions. Properties Alkyl halides have a dipole moment. They are poorly soluble in water, but dissolve in organic solvents. They react as electrophiles at the carbon center. Reactions Alkyl halides undergo nucleophilic substitution reactions and elimination reactions. Spectroscopic analysis The presence of a halogen atom can be shown by IR spectroscopy (C–X stretching absorptions) as well as by mass spectrometry. The latter shows a characteristic pattern of peaks for the molecular ion that matches the number and ratio of naturally occurring isotopes of the halogen. Elemental analysis also demonstrates the presence of halogens. Related topics (A3) sp 3 Hybridization (C3) Intermolecular bonding (C4) Properties and reactions (H3) Electrophilic addition to symmetrical alkenes (M4) Reactions of alcohols (P3) Infra-red spectroscopy (P4) Proton nuclear magnetic resonance spectroscopy (P6) Mass spectrometry Preparation Alkenes can be treated with hydrogen halides (HCl, HBr, and HI) or halogens (Cl 2 and Br 2) to give alkyl halides and dihaloalkanes respectively (Section H3)...
- Robert J. Farrauto, Lucas Dorazio, C. H. Bartholomew(Authors)
- 2020(Publication Date)
- Wiley-AIChE(Publisher)
...CHAPTER 9 HYDROGENATION, DEHYDROGENATION, AND ALKYLATION 9.1 INTRODUCTION Selective catalytic hydrogenation of functional groups contained in organic molecules is one of the most useful, versatile, and environment-acceptable reaction routes available for organic synthesis. This important area of catalytic chemistry has been and continues to be the foundation for the development of numerous, diverse, largeand small-scale commercial hydrogenation processes, including (i) fine chemicals, (ii) intermediates for the pharmaceutical industry, (iii) monomers for the production of various polymers, and (iv) fats and oils for edible and nonedible products. Dehydrogenation reactions find a wide application in production of hydrogen, alkenes, polymers, and oxygenates. In recent years, the demand for light alkenes has grown dramatically due to increased demand for polypropylene, acrylonitrile, oxo alcohols, and propylene oxide. As a result, dehydrogenation of lower alkanes to alkenes is a rapidly expanding business. Alkylation allows smaller molecules to be coupled to for larger molecules mostly for petroleum applications. 9.2 HYDROGENATION 9.2.1 Hydrogenation in Stirred Tank Reactors With exception of a few continuous hydrogenation processes in petroleum refining, hydrogenation processes are often conducted in stirred tank reactors. This chapter focuses on hydrogenation occurring within stirred tank reactors, which are ideally suited and extensively used for liquid-phase hydrogenation reaction. For reactions where the hydrocarbon to be hydrogenated is in the liquid phase, stirred tank reactors are ideal. For hydrogenation, stirred tank reactors can be designed in two configurations, semibatch and continuous, which are illustrated in Figure 9.1...
eBook - ePub- Katarzyna Staszak, Karolina Wieszczycka, Bartosz Tylkowski, Katarzyna Staszak, Karolina Wieszczycka, Bartosz Tylkowski(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
...di-, tri-, chlorobenzene with different positions of the halogene atoms attached to the benzene ring could be formatted. Sandmeyer reaction [ 14 ]: –diazonium salt reacts with copper salts as reagents or catalysts: S: Carboxylic acids or esters P: Acyl halogens Directly reaction of carboxylic acids or esters [ 15 ] with source of halogens, i.e. thionyl chloride (SOCl 2), phosphorus trichloride (PCl 3), phosphorus pentachloride (PCl 5): Depending on the type of organic halogen compounds, different ways of synthesis (see Table 7.1), as well as different technologies, are proposed in the literature and industry, which will be discussed, in detail, in the following sections. Particular attention was given to the compounds with the widest industrial applications. 7.2 Alkyl halides Alkyl halides, known as haloalkanes, are a group of organic chemical compounds derived from alkanes in which one or more hydrogen atoms have been replaced by a halogen atom (see Figure 7.1). Similar to alcohols, alkyl halides could be divided into different classes depending on how the halogen atom is positioned on the chain of carbon atoms: i. primary alkyl halides (RCH 2 X), ii. secondary alkyl halides (R 2 CHX) and iii. tertiary alkyl halides (R 3 CX). 7.2.1 Chloromethanes The simplest example of haloalkanes is chloromethane (known also as methyl chloride, Refrigerant-40, R-40 or HCC 40). In industrial practice, two methods of its synthesis are applied: chlorination of CH 4 or hydrochlorination of methanol. Global chloromethane market was esteemed at 1.8 billion US$ in 2017 and is expected to reach 2.5 billion US$ in 2026, at a CAGR of 4.21 % during a forecast period [ 16 ]. Due to ta cascade reaction in chlorination process, the other products are also obtained: dichloromethane, chloroform, and carbon tetrachloride. From the practical point of view, generally synthesis of all compounds is realized in the industry process simultaneously...
