Various methods of organic synthesis of nitro compounds

There are seemingly many different ways in which amines can be prepared.

A nitro compound ordinarily is made by the reaction, called nitration, between nitric acid and an organic compound. Nitration of aromatic compounds, such as benzene or toluene, is commonly effected by treating them with a mixture of nitric and sulfuric acids at temperatures of 100В° C or lower. These temperatures are not high enough for nitrating aliphatic compounds; propane, however, is commercially converted to a mixture of nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane by allowing it to react with nitric acid vapours at temperatures of about 400В° C. The mixture is then separated into its components by fractional distillation.

The most important reaction of aromatic nitro compounds is their reduction, which can be brought about by a wide variety of agents. Under acidic conditions, reduction almost always produces an amine. In neutral media, reduction may yield a hydroxylamine. In alkaline solution, compounds containing nitrogen-to-nitrogen bonds (azo, hydrazo, or azoxy compounds) are formed.

Hydrolysis of aliphatic nitro compounds is also widely used. Primary aliphatic nitro compounds can be converted to aldehydes by treatment of their carbanion salts with sulphuric acid. When primary nitro compounds are treated with H2SO4 without prior conversion to salts, they give carboxylic acids. Secondary nitro alkanes hydrolyze with boiling HCl to give ketones and nitrous oxide.

Amino groups are particularly susceptible to reactions with a wide variety of reagents, especially oxidizing reagents, alkylating reagents, and many carbonyl compounds. Therefore, if we wish to prevent the amino group from undergoing undesired reactions while chemical change occurs elsewhere in the molecule, it must be suitably protected (protonation. alkylation, acylation, sulfonylation).

ВAmides generally are formed from acid chlorides, acid azides, acid anhydrides, and esters. It is not practical to prepare them directly from an amine and a carboxylic acid without strong heating or unless the reaction is coupled to a second reaction that "activates" the acid.

The hydrolysis of nitriles is a satisfactory method for preparation of unsubstituted amides and is particularly convenient when hydrolysis is induced underВ mildly basic conditions by hydrogen peroxide.

A nitrile is any organic compound that has a �C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in the latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.

REVISION EXERCISES

Ex.1. Answer the following questions:

1. What is a nitro compound? 2. What are physical properties of nitro compounds? 3. What is indicated by Arabic number? 4. Why are nitro compounds commercially produced? 5. What are amines? 6. What is the difference between aliphatic or aromatic compounds? 7. What are physical properties of amines? 8. What are amides? 9. Which methods of organic synthesis of nitro compounds are the most widely used? 10. What is a nitrile?

Ex.2. Match the words with their definitions:

1. alkaloid	a. a substance that can cause cancer
2. antibiotic	b. the opposite of oxidation
3. derivative	c. smth. that involves the sharing of electron pairs between atoms.
4. carcinogen	d. a drug that is used to kill bacteriaand cure infections
5. covalent bond	e. to improve something:
6. fractional distillation	f. a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms.
7. enhance	g. something that has developed or been produced from something else
8. reduction	h. the separation of a mixture into its component parts

Ex.3. Say whether the following statements are true or false:

1. The types of nitrogen compounds are so rare and unique that know all of them by heart. 2. The boiling points of nitro compounds differ from those of other compounds of same molecular mass. 3. All nitro compounds are readily soluble in water. 4. Nitro compounds are widely used in industry. 5. Alkaloids are basic organic amines mostly of plant origin. 6. Essential vitamins and hormones don’t contain any nitrogen in its composition.7. Amines normally have very pleasant smell of bitter almonds. 8. Everybody who studies peptides and proteins should know a lot about the chemistry of simple amides. 9. Hydrolysis of aliphatic nitro compounds is the most expensive and unpopular way of organic synthesis of nitro compounds.

Ex.4. Insert the necessary word:

1. Nitroglycerine … firstВ by Ascanio Sobrero, an Italian chemist at the University of Turin. 2. Like nitrocellulose, nitroglycerine can be thought of as a glycerol-… with nitro-groups. 3. The addition of sulfuric acid and nitric acid to glycerol leads to the O-nitration of glycerol, whereby the nitro-group … the protons of glycerol’s hydroxyl groups. 4. However, unlike nitrocellulose nitroglycerin’s molecular make up … it to exothermically decompose into gases without an external oxygen source; rather than deflagrating, nitroglycerin detonates. 5. Unfortunately, the … of nitroglycerine has a very low activation energy barrier; which makes nitroglycerine susceptible to explosion upon physical contact, and thus impractical for use in most contexts. 6. By 1867, however, Alfred Nobel was able to calm the shock sensitivity of nitroglycerin…. (was synthesized,В allows, derivative, replaces, to produce dynamite, combustion.В)

 

Unit IXВВВ Alcohols

The products of replacement of hydrogen in hydrocarbons by the hydroxyl group (hydroxyl group) are known as alcohols. The general formula for an alcohol is ROH, the R representing the aliphatic portion of the molecule, alcohols may be regarded as derivatives of water in which an alkyl group replaces one hydrogen atom. The alcohols bear some physical resemblance both to the hydrocarbons and water. The best known member of the class is ethyl alcohol, CH₃CH₂OH. It is soluble both in water and in gasoline. Its boiling point is lower than that of water, although its molecular weight is much greater.

The hydroxyl derivatives of aromatic hydrocarbons are called aromatic alcohols when the hydroxyl group is in the side chain and phenols when the hydroxyl group is attached directly to a benzene ring.

Aliphatic alcohols are divided into saturated and unsaturated ones in conformity with the nature of the hydrocarbon radical.

The characteristic functional group of alcohols is hydroxyl or –OH group. Depending on the number of –OH groups in the molecule the alcohols are classified into monohydric, dihydric, trihydric, and polyhydric alcohols.

The isomerism of alcohols is caused by the structure of the radical (isomerism of the carbon skeleton) and the position of the hydroxyl (position isomerism). There are primary I, secondary II, and tertiary III alcohols in conformity with the position of the hydroxyl in the molecule, depending on the carbon (primary, secondary, or tertiary one) with which it is linked.

There are several general methods of alcohol preparation:

1. The hydration of olefins in the acid medium. This method is of great importance, because it allows us to obtain alcohols from gases of petroleum cracking. Primary alcohol, or ethanol, is obtained from ethylene, while only secondary and tertiary alcohols are obtained from other olefins. The method of direct hydration is used industrially; it is carried out by passing a mixture of olefin and water vapour over a phosphate catalyst.

2. Another important industrial method is the fermentation of carbohydrates.

3. Hydrolysis of the halogen derivatives. This method is important in obtaining alcohols from hydrocarbons.