Bromoethane
Encyclopedia
Bromoethane, also known as ethyl bromide, is a chemical compound
of the haloalkane
s group. It is abbreviated by chemists as EtBr. This volatile compound has an ether-like odour.
to ethene:
Ethyl bromide is inexpensive and would rarely be prepared in the laboratory. A laboratory synthesis include the reacting ethanol
with a mixture of hydrobromic
and sulfuric acid
s. An alternate route involves refluxing ethanol with phosphorus
and bromine
; phosphorus tribromide
is generated in situ.
, EtBr is the synthetic equivalent of the ethyl carbocation
(Et+) synthon
. In reality, such a cation is not actually formed. For example, carboxylates salts are converted to ethyl ester
s, carbanion
s to ethylated derivatives, thiourea into ethylisothiouronium salts, and amine
s into ethylamines.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of the haloalkane
Haloalkane
The haloalkanes are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and...
s group. It is abbreviated by chemists as EtBr. This volatile compound has an ether-like odour.
Preparation
The preparation of EtBr stands as a model for the synthesis of alkyl bromides in general. It is usually prepared by the addition of HBrHydrogen bromide
Hydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and...
to ethene:
- H2C=CH2 + HBr → H3C-CH2Br
Ethyl bromide is inexpensive and would rarely be prepared in the laboratory. A laboratory synthesis include the reacting ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
with a mixture of hydrobromic
Hydrobromic acid
Hydrobromic acid is a strong acid formed by dissolving the diatomic molecule hydrogen bromide in water. "Constant boiling" hydrobromic acid is an aqueous solution that distills at 124.3 °C and contains 47.6% HBr by weight, which is 8.89 mol/L. Hydrobromic acid has a pKa of −9, making it a...
and sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
s. An alternate route involves refluxing ethanol with phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
and bromine
Bromine
Bromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
; phosphorus tribromide
Phosphorus tribromide
Phosphorus tribromide is a colourless liquid with the formula PBr3. It fumes in air due to hydrolysis and has a penetrating odour. It is widely used in the laboratory for the conversion of alcohols to alkyl bromides.-Preparation:...
is generated in situ.
Uses
In organic synthesisOrganic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
, EtBr is the synthetic equivalent of the ethyl carbocation
Carbocation
A carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability . Therefore carbocations are often reactive,...
(Et+) synthon
Synthon
A synthon is a concept in retrosynthetic analysis. It is defined as a structural unit within a molecule which is related to a possible synthetic operation. The term was coined by E.J. Corey...
. In reality, such a cation is not actually formed. For example, carboxylates salts are converted to ethyl ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s, carbanion
Carbanion
A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons. The carbanion exists in a trigonal pyramidal geometry. Formally a carbanion is the conjugate base of a carbon acid.where B...
s to ethylated derivatives, thiourea into ethylisothiouronium salts, and amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
s into ethylamines.