10th Class Science Carbon and its Compounds / कार्बन और उसके यौगिक Functional Groups

        Functional Groups

A group of compound which determines the property of the hydrocarbon is called functional group. Particular types of reactions are associated with the functional groups with different structural attachments, resulting to names associated with such compounds.

The carbonyl group is the functional group involved with several of the hydrocarbon derivatives shown above. The carboxyl group is present in amino acids and carboxylic acids.

In chemistry, an alcohol is any organic compound in which a hydroxyl functional group (-OH) is bound to a carbon atom, usually connected to other carbon or hydrogen atoms. An important class are the simple acyclic alcohols, the general formula for which is\[{{C}_{n}}{{H}_{2n+1}}OH\] . Of those, ethanol \[({{C}_{2}}{{H}_{5}}OH)\] is the type of alcohol found in alcoholic beverages, and in common speech the word alcohol refers specifically to ethanol. 

• Simple Alcohols

The most commonly used alcohol is ethanol, \[{{\mathbf{C}}_{\mathbf{2}}}{{\mathbf{H}}_{\mathbf{5}}}\mathbf{OH}\]. Ethanol has been produced and consumed by humans for millions of years, in the form of fermented and distilled alcoholic beverages. It is a clear flammable liquid that boils at 78.4 °C, which is used as an industrial solvent, car fuel, and raw material in the 

chemical industry. In many countries, because of legal and tax restrictions on alcohol consumption, ethanol destined for other uses often contains additives that make it unpalatable poisonous. Ethanol in this form is known generally as denatured alcohol. When methanol is used, it may be referred to as methylated spirits.                                                                 

Methanol \[{{(C{{H}_{3}}OH)}^{-}}\] Wood alcohol, Ethanol \[{{({{C}_{2}}{{H}_{5}}OH)}^{-}}\] Grain alcohol, IsopropyI alcohol \[{{({{C}_{3}}{{H}_{7}}OH)}^{-}}\] Rubbing alcohol, Pentanol \[{{({{C}_{5}}{{H}_{11}}OH)}^{-}}\] Amyl alcohol, Hexadecan-1-ol (C^H^OH)- Cetyl alcohol, Polyhydric alcohols  \[{{C}_{2}}{{H}_{4}}{{(OH)}_{2}}^{-}\] Ethane-1 ,2-diol, Ethylene glycol \[{{C}_{3}}{{H}_{5}}{{(OH)}_{3}}\] Propane-1,2,3-triol, Glycerin \[{{C}_{4}}{{H}_{6}}{{(OH)}_{4}}^{-}\] Butane-1,2,3,4-tetraol, Erythritol \[{{C}_{5}}{{H}_{7}}{{(OH)}_{5}}\]-Pentane- 1, 2, 3, 4, 5 - pentol.                                                   

\[\underset{methanol}{\mathop{HO-C{{H}_{3}}}}\,\]    \[\underset{ethanol}{\mathop{HO-C{{H}_{2}}-C{{H}_{3}}}}\,\] \[\underset{1-propanol}{\mathop{HO-C{{H}_{2}}-CH-C{{H}_{3}}}}\,\]

\[\underset{\text{1-octanol}}{\mathop{HO-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{2}}-C{{H}_{3}}}}\,\]

\[\underset{\text{2-methyl-1-butanol}}{\mathop{HO-C{{H}_{2}}-\underset{\begin{smallmatrix}

 | \\

 C{{H}_{3}}

\end{smallmatrix}}{\mathop{C}}\,H-C{{H}_{2}}-C{{H}_{3}}}}\,\]                \[\underset{\text{isoamyl}\,\text{alcohol}}{\mathop{HO-C{{H}_{2}}-C{{H}_{2}}-CH-C{{H}_{3}}}}\,\]

              Physical Properties

• Alcohols have an odor that is often described as "biting" and as "hanging" in the nasal passages.
• In general, the hydroxyl group makes the alcohol molecule polar. Those groups can form hydrogen bonds to one another and to other compounds. This hydrogen bonding means that alcohols can be used as protic solvents. Two opposing solubility trends in alcohols are: the tendency of the polar OH to promote solubility in water, and the tendency of the carbon chain to resist it. Thus, methanol, ethanol, and propanol are miscible in water because the hydroxyl group wins out over the short carbon chain.
• Butanol, with a four-carbon chain, is moderately soluble because of a balance between the two trends.
• Alcohols of five or more carbons such as Pentanol and higher are effectively insoluble in water because of the hydrocarbon chain's dominance.
• All simple alcohols are miscible in organic solvents.
• Alcohols can also undergo oxidation to give aldehydes, ketones, or carboxylic acids.
• They can be dehydrated to alkenes.

They can react to form ester compounds, and they can undergo nucleophilic substitution reactions. The lone pairs of electrons on the oxygen of the hydroxyl group also makes alcohols nucleophiles.

           Applications

• Alcohols can be used as a beverage (ethanol only), as fuel and for many scientific, medical, and industrial utilities.
• Ethanol in the form of alcoholic beverages has been consumed by humans since pre- historic times.
• A 50% v/v solution of ethylene glycol in water is commonly used as an antifreeze.
• Some alcohols, mainly ethanol and methanol, can be used as an alcohol fuel.
• Fuel performance can be increased in forced induction internal combustion engines by injecting alcohol into the air intake after the turbocharger or supercharger has pressurized the air. This cools the pressurized air, providing a denser air charge, which allows for more fuel, and therefore more power.
• Alcohols have applications in industry and science as reagents or solvents.
• Because of its low toxicity and ability to dissolve non-polar substances, ethanol can be used as a solvent in medical drugs, perfumes, and vegetable essences such as vanilla. In organic synthesis, alcohols serve as versatile intermediates.
• Ethanol can be used as an antiseptic to disinfect the skin before injections are given, often along with iodine.                       
• Ethanol-based soaps are becoming common in restaurants and are convenient because they do not require drying due to the volatility of the compound. 
• Alcohol is also used as a preservative for specimens.
• Alcohol gels have become common as hand sanitizers.

        Production

In industry, alcohols are produced in several ways:

• By fermentation using glucose produced from sugar from the hydrolysis of starch, in the presence of yeast and temperature of less than 37 °C to produce ethanol, for instance, the conversion of invertase to glucose and fructose or the conversion of glucose to zymase and ethanol.
• By direct hydration using ethylene or other alkenes from cracking of fractions of distilled crude oil.

              Etherification

To form an ester from an alcohol and a carboxylic acid the reaction, known as esterification, is usually performed at reflux with a catalyst of concentrated sulpuric acid:

\[R-OH+R'-COOH\to R'-COOR+{{H}_{2}}O\]

In order to drive the equilibrium to the right and produce a good yield of ester, water is usually removed, by an excess of \[{{H}_{2}}S{{O}_{4}}\]. Esters may also be prepared by reaction of the alcohol with an acid chloride in the presence of a base such as pyridine.

          Oxidation

Primary alcohols \[(R-C{{H}_{2}}-OH)\] can be oxidized either to aldehydes \[(R-CHO)\] or to carboxylic acids \[(R-C{{O}_{2}}H)\] while the oxidation of secondary alcohols \[({{R}_{1}}{{R}_{1}}CH-OH)\] normally terminates at the ketone  \[({{R}_{1}}{{R}_{2}}C=O)\] stage.

Tertiary alcohols \[({{R}_{1}}{{R}_{2}}{{R}_{3}}C-OH)\] are resistant to oxidation. The direct oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde.

It is then transformed via an aldehyde hydrate \[(R-CH{{(OH)}_{2}})\] by reaction with water before, it can be further oxidized to the carboxylic acid.

              Carboxylic Acids

The organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is \[R-COOH,\] where R is some monovalent functional group. A carboxyl group is a functional group consisting of a carbonyl \[(RR'C=O)\] and a hydroxyl \[(R-O-H)\] which has the formula, usually written as \[-COOH\] or -\[C{{O}_{2}}H\].

Other important natural examples are citric acid in lemons and tartaric acid in tamarinds.

Salts and esters of carboxylic acids are called carboxylates. Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide. Under some circumstances they can be decarboxylated to yield carbon dioxide

            Physical properties

• Carboxyfic acids are polar Because they are both hydrogen-bond acceptors (the carbonyl) and hydrogen-bond donors (the hydroxyl); they also participated in hydrogen bonding. Together the hydroxyl and carbonyl group forms the functional group carboxyl. Carboxyfic acids usually exist as dimeric pairs in nonpolar media due to their tendency to "self-associate." Smaller carboxylic acids (1 to 5 carbons) are soluble with water, whereas higher carboxylic acids are less soluble due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be rather soluble in less-polar solvents such as ethers and alcohols.
• Carboxylic acids tend to have higher boiling points than water, not only I because of their increased surface area, but because of their tendency to form stabilized dimers. Carboxylic acids tend to evaporate or boil as these dimers. For boiling to occur, either the dinner bonds must be broken, or the entire dimer arrangement must be vaporized.                   
• Carboxylic acids are typically weak acids, meaning that they only partially dissociate into H+ cations and RCOGr anions in neutral aqueous solution. For example, at room temperature, only 0.4% of all acetic acid molecules are dissociated. Electronegative substituent’s give stronger acids.
• Carboxylic acids often have strong odors, especially the volatile derivatives. % Most common are acetic acid (vinegar) and butanoic acid (rancid butter). On the other hand, esters of carboxylic acids tend to have pleasant odors and many are used in perfumes. 

          Ethanoic Acid

Acetic acid is an organic compound with the chemical formula \[C{{H}_{3}}COOH\]. It is a colourless liquid, that when undiluted is also called glacial acetic acid. As the main component of vinegar, it has a distinctive sour taste and pungent smell. Although it is classified as a weak acid, acetic acid is highly dangerous to skin.

            Chemical Properties

           Reaction of Acetic Acid with Methanol

Acetic acid reacts with methanol in presence of acid catalyst to gives easter.

Ethanoid acid            Ethanol                        Ethyl ethanoate   

            Reaction of Acetic Acid Bose

Ethanoic acid reacts with sodium hydrogen carbonate to given sodium acetate with evolution of carbon dioxide and water.  

              Occurrence and Applications

• Many carboxylic acids are produced industrially on a large scale. They are also pervasive in nature. Esters of fatty acids are the main components of lipids and polyamides of amino carboxylic acids are the main components of proteins.
• Carboxylic acids are used in the production of polymers, pharmaceuticals, solvents, and food additives.
• Industrially important carboxylic acids include acetic acid (component of vinegar, precursor to solvents and coatings), acrylic and methacrylic acids (precursors to polymers, adhesives), adipic acid (polymers), citric acid
• (beverages), ethylenediaminetetraacetic acid (chelating agent), fatty acids (coatings), maleic acid (polymers), propionic acid (food preservative), terephthalic acid (polymers).

           Synthesis

• Industrial routes to carboxylic acids generally differ from those used on smaller scale, because they require specialized equipment.
• Oxidation of aldehydes with air using cobalt and manganese catalysts. The required aldehydes are readily obtained from alkenes by hydroformylation.
• Oxidation of hydrocarbons using air. For simple alkanes, the method is nonselective but so inexpensive to be useful. Allylic and benzylic compounds undergo more selective oxidations.

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