Alkynes

• Contains c to c triple bonds.• Alkynes can be described by the formula CnH2n - 2where n is

2,3, ……• The simplest member of this homologous series has the

molecular formula C2H2

• where R may be an alkyl group or H• Alkynes are very reactive compounds and hence they never

occur in the free state in nature. They are present to a sizeable extent in the gases obtained by the cracking of petroleum

Preparation of ethyne in the laboratory

• Ethyne is prepared by the action of water on calcium carbide.

The gas thus produced is collected by the downward displacement of water.

properties• Physical properties• It is a colourless gas with garlic-like odour when pure.

It is soluble in organic solvents. It is poisonous and highly explosive.

• Chemical properties1. Combustion• It burns in air with a sooty flame to produce carbon

dioxide and water vapour. The flame is white, sooty and produces an extremely high temperature of 40000C.

Chemical properties

2. Addition reactionsDue to higher degree of unsaturation, addition

reaction in ethyne takes place in 2 stages:1. The 1st stage yields a product with c = c2. The 2nd stage converts this into a fully

saturated compound. i.e. c - c

Chemical properties

2 (a) Addition of hydrogen• An ethyne reacts with hydrogen in the

presence of catalyst (Pt or Ni) at 250°C, first forming ethene and finally ethane.

b. With Halogens (e.g chlorine/bromine)

Stage I Stage II

I and II combined

Try for bromine (Br2)

c. With the hydrogen halides (HCl, HI, HBr)

Chemical ppties (addition rxn)

d. With chlorine and bromine water (HOCl & HOBr)

e. Addition of waterIn the presence of sulphuric acid (42%) and 1 % mercuric sulphate at 60°C, ethyne add on one water molecule to give ethanal.

dichloroethanal

ethanal

Xcal ppties3. Oxidation• acidified KMnO4 oxidises ethyne to oxalic

acid(ethan edioic acid).

4[O]

PolymerizationWhen ethyne (acetylene) is passed through a hot copper tube, it polymerizes to benzene.

Laboratory Detection of Ethyne

• Both ethene and ethyne are unsaturated hydrocarbons and as a result of this, both can decolourise bromine water (HOBr) and acidified potassium tetraoxomanganate (VII) (KMnO4).

• So how can we distinguish between these?

Test to Differentiate btw ethene and ethyne

• Ethyne has the power to undergo certain reactions with the insoluble salts of the noble metals, especially those of copper and silver.

ethyne reacts with ammoniacal copper(I)chlorider(CuCl) To produce reddish brown precipitate

and with silver equivalence which is silver(I)chloride(AgCl).

To produce yellow ppt which rapidly turns grey.While

ethene has no effect on all these salts.

Uses

• Illuminant in acetylene lamps.• Oxy-acetylene torches for welding metals.• Starting material for the synthesis of organic

compounds like acetaldehyde, acetic acid, ethyl alcohol and tetrachloroethane. Tetrachloroethane is a solvent and is also called Westron.

AROMATIC HYDROCARBONS-BENZENE

• A benzene ring is a six-membered ring containing carbon atoms linked to each other with alternate single and double bonds.

• Aromatic hydrocarbons that contain one or more benzene rings are called Arenes (CnH2n-6 )

• Some benzene compounds

(where n = 6 or more).

Structures of benzene

Defects in Kekule's formulaWhile Kekule's formula explained most of theory served facts for benzene, it could still not explain the saturated nature of benzene.

Resonance hybrid structure of benzeneThe currently accepted structure was developed by the application of the theory of resonance proposed in 1933. This theory states that benzene is a resonance hybrid of the following canonical forms.

Kekule's (1865) formula

Properties of Benzene• Physical• Benzene is a colourless liquid (melting point

5.5°C, boiling point 80.4°C) with a characteristic smell of aroma.

• It is immiscible with water, but dissolves organic solutes.

• It is lighter than water: density 0.87 g cm-3

• Its vapors are toxic.

Chemical Properties of Benzene

Properties of Benzene

1. CombustionBenzene and its homologues are highly inflammable liquids and burn with a sooty flame.

2C6H6 + 15O2 12CO2 + 6H2O

2. Substitution reactionsBenzene gives substitution reactions with chlorine as described below.

• Addition Reactions• Benzene gives some addition reactions. Some typical

reactions are:Addition of hydrogen

• Benzene on reduction with hydrogen under pressure in the presence of finely divided nickel at 200°C, gives an addition product hexahydrobenzene (cyclohexane).

Properties of Benzene

Addition of chlorineChlorine adds on to benzene at its boiling point, in the presence of bright sunlight, to give hexachloride.

3Cl2

cyclohexane

benzene hexachloride

Uses of Benzene

1.As an industrial solvent for fats and oils, rubber, resins etc.

2.As a starting material for dyes, drugs, perfumes and explosives and polymers

3.For dry-cleaning of woollen clothes.4.As a motor fuel along with petrol,

under the name benzol.

Alkanols(Saturated Monohydric Alcohols) General formula:

CnH2n +1 OHFunctional group:OHSuffix:ol

They can be classified as:Alcohols with one hydroxyl group - Monohydric alcoholAlcohols with two hydroxyl groups - Dihydric alcoholAlcohols with three hydroxyl groups - Trihydric alcoholsAlcohols with four or more hydroxyl groups - Polyhydric alcohols

No. of C Atoms Molecular formula Parent alkane Common

name IUPAC name

1 CH3OH CH4 (methane) Methyl alcohol Methanol

2 CH3CH2OH C2H6 (ethane) Ethyl alcohol Ethanol

3 C3H7OH C3H8(propane) Propyl alcohol Propanol

4 C4H9OH C4H10(propane) Butyl alcohol Butanol

For example:

They can be further classified into:Primary AlcoholHere the carbon atom bearing the hydroxyl group is attached to just one other carbon atom.

Secondary AlcoholHere the carbon atom bearing the hydroxyl group is attached to two other carbon atoms.

Tertiary AlcoholHere the carbon atom bearing the hydroxyl group is attached to three other carbon atoms.

Ethanol(Kaikai,Ogogoro,sepe)Ethyl alcohol is the most important member of the alcohol series and is otherwise known as alcohol, spirit of wine and grain alcohol. It can be prepared by any one of the general methods of preparation of primary alcohol.

From EthyleneEthylene, obtained from cracked petroleum, is compressed to 11400 - 22800 mm of Hg pressure and absorbed in concentrated sulphuric acid (98%) at 340 - 350K. The resulting product is ethyl hydrogen sulphate or ethyl sulphate.

Preparation

The reaction mixture is diluted with water and warmed. Hydrolysis occurs and ethanol is got along with some ether as by-product.

The ethanol formed is distilled off, leaving the acid which can be concentrated and used again.

Manufacture of Ethanol by Fermentation

Ethanol can be manufactured by the fermentation of:MolassesStarch. (maize (US: corn), wheat, barley or potatoes.)

Fermentation is slow decomposition by micro-organisms of large organic molecules into smaller moleculesThis is the principle behind souring of milk, batter, putrefaction of meat, and preparation of wine and vinegar.Fermentation was the earliest method used for preparing alcohol in industries. This is still used for the manufacture of alcohol and alcoholic drinks like beer, wine, brandy, etc,.

Assignment: find out the process of manufacturing of ethanol from molasses

From StarchStarchy raw materialsWheat, barley, rice, maize and potatoes.

Conversion of starch into maltose (saccharification) It is carried out as follows:Step IMaltingMoist barley is allowed to germinate in dark at 290K. Germinated barley is called Malt and this is heated to 330K (to stop further germination). It is then crushed and extracted with water. This Malt extractcontains the enzyme diastase.Step IIMashingTo break the cell walls, starch is reacted with superheated steam. This exposes the starch inside that forms a paste like mass called Mash.

Conversion of starch into maltose (saccharification)

Step IIIHydrolysisMash and malt extract (supplies enzyme DIASTASE) are treated together at 320-330K. In about half an hour, hydrolysis is complete and maltose is formed.

Step IVAlcoholic FermentationMaltose obtained from starch is fermented in the presence of yeast. Maltase present in yeast converts maltose into glucose. Another enzyme zymase present in yeast, then converts glucose into ethanol and carbon dioxide.

Concentration of ethanol

The ethanol produced by fermentation is 18% pure because yeast cell is killed at concentrations higher than this.

By fractional distillation of the product, concentration of ethanol increases to 95%. This is called rectified spirit.Further purification of rectified spirit by distilling over quicklime yield an ABSOLUTE SPIRIT which contain 99.5% ethanol.

Physical Properties1. Ethanol is a colourless, inflammable liquid has a spirituous

odour and burning taste.2. Ethanol boils at 780C, freezes at -18oC. 3. Mixes with water in all proportions (soluble in water). 4. Neutral to litmus

Note:The boiling point and solubility of alkanols are affected by the presence of hydrogen bonding in alkanols.

HOW?

Hydrogen bondingHydrogen bonding occurs between molecules where you have a hydrogen atom attached to one of the very electronegative elements - fluorine, oxygen or nitrogen.

In the case of alcohols, there are hydrogen bonds set up between the slightly positive hydrogen atoms and lone pairs on oxygens in other molecules.

The hydrogen atoms are slightly positive because the bonding electrons are pulled away from them towards the very electronegative oxygen atoms.

Hydrogen bonding in alcohols

An alcohol is an organic molecule containing an -O-H group. Any molecule which has a hydrogen atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding.

Such molecules will always have higher boiling points than similarly sized molecules which don't have an -O-H or an -N-H group. The hydrogen bonding makes the molecules "stickier", and more heat is necessary to separate them.

Ethanol, CH3CH2-O-H, and methoxymethane, CH3-O-CH3, both have the same molecular formula, C2H6O.

The boiling points of ethanol and methoxymethane show the dramatic effect that the hydrogen bonding has on the stickiness of the ethanol molecules:

ethanol (with hydrogen bonding) 78.5°C

methoxymethane (without hydrogen bonding)

-24.8°C

The hydrogen bonding in the ethanol has lifted its boiling point about 100°C.

The higher boiling point of the butan-1-ol is due to the additional hydrogen bonding.

Note

Comparing the two alcohols (containing -OH groups), both boiling points are high because of the additional hydrogen bonding due to the hydrogen attached directly to the oxygen - but they aren't the same.

The boiling point of the 2-methylpropan-1-ol isn't as high as the butan-1-ol because the branching in the molecule makes the van der Waals attractions less effective than in the longer butan-1-ol.

Solubility of alcohols in water

Generally, hydrocarbons are not soluble in water, but alkanols are Soluble because the hydroxyl groups in their molecules can form hydrogen bondings with the water molecules.

Solubility decreases as the number of carbon atoms in increases in alkanols. Primary alkanol with more than five carbon atoms are insoluble in water.

Chemical Properties

1 Combustion reactionSupply the equation of reaction

2 With sodium and potassiumWhen sodium, potassium or lithium is reacted with dry ethanol, the hydrogen atom of the hydroxy group is replaced by the metal atom to form alkoxides. Hydrogen is liberated in the process.

This reaction also serves as an identification test for alcohols.

3 Reaction with the chloride of phosphorus

Reaction with phosphorus(III) chloride, PCl3

Alcohols react with liquid phosphorus(III) chloride (also called phosphorus trichloride) to make chloroalkanes.

Reaction with phosphorus(V) chloride, PCl5

Solid phosphorus(V) chloride (phosphorus pentachloride) reacts violently with alcohols at room temperature, producing clouds of hydrogen chloride gas

4. OxidationEthanol is oxidised to acetaldehyde first, which is then oxidised to acetic acid (ethanoic acid). Note:-Note that both the aldehyde and the acid formed contain the same number of carbon atoms as the alcohol

OR

This is what is happening in the second stage:

Secondary alcohols are oxidised to ketones (alkanone).For example, if you heat the secondary alcohol propan-2-ol with sodium or potassium dichromate(VI) solution acidified with dilute sulphuric acid, you get propanone formed.

Tertiary alcohols aren't oxidised by acidified sodium or potassium dichromate(VI) solution. There is no reaction whatsoever.

5. Dehydration

With sulphuric acid (another dehydrating agent), ethanol gives various products under different conditions.With excess concentrated sulphuric acid at temperature above 170oC , ethanol reacts to form ethyl hydrogen tetraoxosulphate(VI) which then decomposes to yield ethene.

170(1)

(2)

On the other hand, if the alkanol is in excess, and the temperature is lower, it will react with the acid to yield ethoxyethane (diethyl ether)

170

6. ESTERIFICATION

Ethanol reacts reversibly with acids to form ethyl esters. This process is known as esterification.

if you were making ethyl ethanoate from ethanoic acid and ethanol, the equation would be:

Ethanol is used in the manufacture of:1. paints and varnishes2. alcoholic beverages3. ether, choloform, iodoform and other organic

compounds dyes 4. power alcohol, a substitute for petrol5. it is also used as a fuel in spirit lamps and stoves6. in scientific apparatus like thermometers and

spirit levels7. Because of is low freezing point (-117oC), ethanol

is sometimes used as an anti-freeze in automobile radiator.

Uses of Ethanol

Ethanol can be identified by the fruity odour it emits when heated gently with sodium acetate and concentrated sulphuric acid. This is due to the formation of ethyl ethanoate. Iodoform test: When a few drops of alcohol is warmed with iodine and potassium hydroxide, of iodoform with characteristic smell is got.

yellow precipitate

Analytical Tests for Ethanol

Reaction with Carboxylic Acids (Esterification)Alcohols react with carboxylic acids in the presence of concentrated sulphuric acid as catalyst to form esters which have generally sweet fruits smells. For example,

This reaction is used as a test for alcohols as well as carboxylic acids.

Analytical Tests for Ethanol

Sodium Metal TestWhen a small piece of sodium metal is dropped into alcohol, hydrogen is liberated. This is accompanied by effervescence.

In this test, the alcohol used must be free from moisture. This is because water reacts with sodium in the same way as alcohol, liberating hydrogen gas. The test could be misleading otherwise.

Alkanoic Acids or Saturated Monocarboxylic AcidGeneral formula: CnH2n+1COOHFunctional group:

Suffix: oic acid

carboxylic (- COOH) group

In IUPAC system, the name of an alkanoic acid is obtained by replacing the last 'e' from the name of the parent alkane with -oic acid.Name of monocarboxylic acid = Name of the parent alkane - e + oic acid= Alkanoic acid

A dicarboxylic acid contains two carboxylic groups linked to the same or different carbon atoms. In the IUPAC system, the name of alkanedioic acid is obtained by adding the suffix, -dioic acid to the name of the parent alkane.Name of the dicarboxylic acid = Name of the parent alkane + dioic acid

For example: Ethanedioic acid (oxalic acid, parent alkane is ethane)

Propanedioic acid (Malonic acid), parent alkane is propane)

Butanedioic acid (Succinic acid, parent alkane is butane)

Ethanoic Acid

Formula: CH3COOH, IUPAC Name: Ethanoic acid

Source: vinegar

Physical propertiesAcetic acid is a colourless, corrosive liquid with a pungent smell at ordinary temperatures. Below 290K, it solidifies to an icy mass called glacial acetic acid. It boils at 391K It is miscible with water, alcohol and ether in all ratios.

THE LAB PREPARATION OF ETHANOIC ACID

It can be prepared by distilling anhydrous sodium ethanoate, CH3COONa with conc. Tetraoxosulphate (VI) acid.

CH3COONa + H2SO4 CH3COOH + NaHSO4

CH3COOH

H2SO4

CH3 COONa

Ice water

Ethanoic acid can also be prepared by the complete oxidation of ethanol by acidified sodium heptaoxodichromate(VI) solution.

CH3CH2OH + 2[O] CH3COOH + H2O

Chemical Properties

Physical propertiesAcetic acid is a colourless, corrosive liquid with a pungent smell at ordinary temperatures. Below 290K, it solidifies to an icy mass called glacial acetic acid. It boils at 391K It is miscible with water, alcohol and ether in all ratios.

Chemical Properties

Acidic propertiesAcetic acid ionizes in polar media to give hydrogen ion that is responsible for its acidic behavior.

So, acetic (ethanoic) acid can react with alkalis and alkali metal carbonates and also with metals. (properties of an acid)

With Alkalis, Carbonates and Bicarbonates

ethanoate

Bicarbonate(hydrogen trioxocarbonate(IV)) test is used as an identification test for the presence of carboxylic group in a compound.

With MetalsAcetic acid reacts with strongly electropositive metals like sodium and zinc to give the respective acetate and liberate hydrogen.

Ester formation(esterification)Ethanoic acid reacts with alcohols (ethanol) in the presence of dehydrating agents like concentrated tetraoxosulphate(VI) acid to form esters.

ethanoate

In the presence of lithium aluminium hydride (LiAlH4 ), ethanoic acid can be reduced to ethanol.

Reduction

Tests for Ethanoic AcidIf the compound is soluble in water and if it gives brisk effervescence (due to the liberation of carbon dioxide) when treated with sodium trioxocarbonate(IV) or sodium hydrogen trioxocarbonate(IV), it is a carboxylic acid.

1. Ethanoic acid is used in the: manufacture of dyes, perfumes and rayons

2. manufacture of rubber from latex and casein from milk. It is used for coagulation

3. form of salts in medicine and paints4. form of acetates of aluminium and chromium is used as

mordants5. dilute form is used as vinegar and in the concentrated form as a

solvent6. form of organic esters as perfumes

Uses of Ethanoic Acid

Mordants are compounds that are used often in the production of various textile products. The main purpose of a mordant is to interact with the fibers of a given material and the dye solution. This interaction helps to ensure that the dye sets properly, without splotching or running. Mordants are employed at several different points in the production process, depending on the type of material used and the desired effect that the manufacturer wishes to achieve.

Ethylenediamminetetraacetate EDTA