Organic Chem Ii

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 disp

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 properties 1. 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 reactions Due to higher degree of unsaturation, addition reaction in ethyne takes place in 2 stages: 1.The 1st stage yields a product with c =c 2.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) S ta g e I

S ta g e II

I a n d II co m b in e d

Try fo r b ro m in e (Br2)

c.

With the hydrogen halides ( HCl , HI , HBr )

Chemical ppties (addition rxn) d. With chlorine and bromine water (HOCl & HOBr)





d ich lo ro e th a n a e . A d d itio n o f w a te r l In th e p re se n ce o f su lp h u ric a cid ( 4 2 % ) a n d 1 % m e rcu ric su lp h a te a t 6 0 ° C , e th yn e a d d o n o n e w a te r m o le cu le to g ive e th a n a l.

e th a n a l

Xcal ppties

3. Oxidation • acidified KMnO4 oxidises ethyne to oxalic acid(ethan edioic acid). • 4[ 

O]

P o ly m e riza tio n W h e n e th yn e ( a ce tyle n e ) is p a sse d th ro u g h a h o t co p p e r tu b e , it p o lym e rize s to b e n ze n e .

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 eof copper th yn e re a cts wand ith a m silver. m o n ia ca l co p p e r( I) ch lo rid e r( C u C l) To p ro d u ce re d d ish b ro w n p re cip ita te a n d w ith silve r e q u iva le n ce w h ich is silve r( I) ch lo rid e ( A g C l). To p ro d u ce y e llo w p p t w h ich ra p id ly tu rn s g re y . W h ile e th e n e h a s n o e ffe ct o n a llth e se sa lts.  

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 ( where Arenes n = 6 or m o re ). (CnH2n-6  ) • • Some benzene compounds •

Structures of benzene K e k u le 's  ( 1 8 6 5 ) fo rm u la D e fe cts in K e k u le 's fo rm u la W h ile K e ku le 's fo rm u la exp la in e d m o st o f th e o ry se rve d fa cts fo r b e n ze n e , it co u ld still n o t exp la in th e sa tu ra te d n a tu re o f b e n ze n e . R e so n a n ce h y b rid stru ctu re o f b e n ze n e T h e cu rre n tly a cce p te d stru ctu re w a s d e ve lo p e d b y th e a p p lica tio n o f th e th e o ry o f re so n a n ce p ro p o se d in 1 9 3 3 . T h is th e o ry sta te s th a t b e n ze n e is a re so n a n ce h yb rid o f th e fo llo w in g ca n o n ica lfo rm s.

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. •

Properties of Benzene Chemical Properties of Benzene 1 . Combustion Benzene and its homologues are highly inflammable liquids and burn with a sooty flame. 2C6H6 + 15O2

12CO2 + 6H2O

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

Properties of Benzene • 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). • cyclohexane

A d d itio n o f ch lo rin e C h lo rin e a d d s o n to b e n ze n e a t its b o ilin g p o in t, in th e p re se n ce o f b rig h t su n lig h t, to g ive h exa ch lo rid e . 3Cl2

benzene hexachloride

Uses of Benzene

n t fo r fa ts a n d o ils, ru b b e r, re sin s e t lfo r d ye s, d ru g s, p e rfu m e s a n d exp l o o lle n clo th e s. w ith p e tro l, u n d e r th e n a m e b e n zo l

Alkanols(Saturated Monohydric Alcohols) General formula : C H    OH   Functional group : n 2n +1

OH Suffix : ol

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

No. of C Atoms

Molecular Parent formula alkane

1

CH3OH

2 3 4

For example:

Common name

CH4 (metha Methyl alcohol ne) CH3CH2O C2H6 (ethanEthyl alcohol H e) C3H7OH C3H8(propa Propyl alcohol ne) C4H9OH C4H10 (prop Butyl alcohol ane)

IUPAC name Methanol Ethanol Propanol Butanol

They can be further classified into:

P rim a ry A lco h o l H e re th e ca rb o n a to m b e a rin g th e h yd roxylg ro u p is a tta ch e d to ju st o n e o th e r ca rb o n a to m .

S e co n d a ry A lco h o l H e re th e ca rb o n a to m b e a rin g th e h yd roxyl g ro u p is a tta ch e d to tw o o th e r ca rb o n a to m s.

Te rtia ry A lco h o l H e re th e ca rb o n a to m b e a rin g th e h yd roxylg ro u p is a tta ch e d to th re e o th e r ca rb o n a to m s.

Ethanol(Kaikai,Ogogoro,sep e)

E th yl a lco h o l is th e m o st im p o rta n t m e m b e r o f th e a lco h o l se rie s a n d is o th e rw ise kn o w n a s a lco h o l, sp irit o f w in e a n d g ra in a lco h o l. It ca n b e p re p a re d b y a n y o n e o f th e g e n e ra lm e th o d s o f p re p a ra tio n o f p rim a ry a lco h o l.

Pre p a ra tio n F ro m E th y le n e E th yle n e , o b ta in e d fro m cra cke d p e tro le u m , is co m p re sse d to 1 1 4 0 0 - 2 2 8 0 0 m m o f H g p re ssu re a n d a b so rb e d in co n ce n tra te d su lp h u ric a cid ( 9 8 % ) a t 340 - 350K. T h e re su ltin g p ro d u ct is e th ylh yd ro g e n su lp h a te o r e th yl su lp h a te . T h e re a ctio n m ixtu re is d ilu te d w ith w a te r a n d w a rm e d . H yd ro lysis o ccu rs a n d e th a n o lis g o t a lo n g w ith so m e e th e r a s b y - p ro d u ct.

T h e e th a n o l fo rm e d is d istille d o ff, le a vin g th e a cid w h ich ca n b e co n ce n tra te d a n d u se d a g a in .

Manufacture of Ethanol by Fermentation

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

rmentation is slow decomposition by micro-organisms of large ganic molecules into smaller molecules This 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 Starch

Starchy raw materials Wheat, barley, rice, maize and potatoes. Conversion of starch into maltose ( saccharification )   It is carried out as follows: Step I Malting Moist 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 extract contains the enzyme diastase. Step II Mashing To 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 III Hydrolysis Mash 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 IV Alcoholic Fermentation Maltose 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

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

tional distillation of the product, concentration of ethanol es to 95%. This is called rectified spirit. purification of rectified spirit by distilling over quicklim LUTE SPIRIT which contain 99.5% ethanol.

Physical Properties

1.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

: boiling point and solubility of alkanols are affected by the ence of hydrogen bonding in alkanols.

HOW?

Hydrogen bonding

Hydrogen 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 ØAn alcohol is an organic molecule containing an -OH group. Any molecule which has a hydrogen atom attached directly to an oxygen or a nitrogen is capable of hydrogen bonding. ØSuch 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. ØEthanol, 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.

Note

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

erally, hydrocarbons are not soluble in water, but alkanols ar uble because the hydroxyl groups in their molecules can form rogen bondings with the water molecules.

lubility decreases as the number of carbon atoms in increases kanols. Primary alkanol with more than five carbon atoms are soluble in water.

Chemical Properties

1 Combustion reaction Supply the equation of reaction 2 With sodium and potassium When 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 phospho Reaction with phosphorus ( III ) chloride , PCl 3 Alcohols react with liquid phosphorus(III) chloride (also called phosphorus trichloride) to make chloroalkanes. Reaction with phosphorus ( V ) chloride , PCl 5 Solid phosphorus(V) chloride (phosphorus pentachloride) reacts violently with alcohols at room temperature, producing clouds of hydrogen chloride gas

4 . Oxidation Ethanol 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.

(1 )

(2 )

170

e other hand, if the alkanol is in excess, and the temperature , it will react with the acid to yield ethoxyethane (diethyl 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:

Uses of Ethanol Ethanol is used in the manufacture of: 1.paints and varnishes 2.alcoholic beverages 3.ether, choloform, iodoform and other organic compounds dyes 4.power alcohol, a substitute for petrol 5.it is also used as a fuel in spirit lamps and stoves 6.in scientific apparatus like thermometers and spirit levels 7.Because of is low freezing point (-117oC), ethanol is sometimes used as an antifreeze in automobile radiator.

Analytical Tests for 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 yellow with iodine and potassium hydroxide , of iodoform with characteristicprecipitate smell is got. 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 Test When 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 Acid General formula : C n H 2n+1 COOH carboxylic (- COOH) group Functional group : Suffix : oic acid

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 Butanedioic ), acid (Succinic parent alkane is propane) acid, parent alkane is butane)

Ethanoic Acid Formula: CH3COOH, IUPAC Name: Ethanoic acid Source: vinegar Physical properties qAcetic acid is a colourless, corrosive liquid with a pungent smell at ordinary temperatures. qBelow 290K, it solidifies to an icy mass called glacial acetic acid. qIt boils at 391K qIt is miscible with water, alcohol and ether in all ratios.

THE LAB PREPARATION OF ETHANOIC ACID

can be prepared by distilling anhydrous sodium ethanoate, 3COONa with conc. Tetraoxosulphate (VI) acid. CH3COONa

+

H2SO4

CH3COOH

H2SO4

CH 3

CO ON a

Ice water

CH3COOH

+

NaHSO4

thanoic acid can also be prepared by the complete oxidation o thanol by acidified sodium heptaoxodichromate(VI) solution. CH3CH2OH H2O

+

2[O]

CH3COOH

+

Chemical Properties

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

Chemical Properties Acidic properties Acetic 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 Metals Acetic 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

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

Tests for Ethanoic Acid If 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.

Uses of Ethanoic 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 paints 4.form of acetates of aluminium and chromium is used as mordants 5.dilute form is used as vinegar and in the concentrated form as a solvent 6.form of organic esters as perfumes

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.

Ethylenediamminetetraacetat e EDTA