CAPE CHEMISTRY UNIT II MODULE I

CAPE CHEMISTRY UNIT II MODULE I

Alcohols and phenol and Alkenes Worksheet and Revision guide

1. First part of homework - Due October 3, 2008(a) Describe the reaction of butan-2-ol with iodine in sodium hydroxide.

(b) Describe the reaction between phenol and sodium hydroxide

2. Classwork (websites for additional notes included with each section)(a) The structure of alcohols

Alkyl group- + -OH

Oxygen more electronegative than carbon and hydrogen

C is INCLUDEPICTURE "http://www.chemguide.co.uk/mechanisms/nucsub/delta.GIF" \* MERGEFORMATINET

+, H is + and O is -

Note bent structure around O which have 2 lone pairs

(b) Classes of alcoholhttp://www.chemguide.co.uk/organicprops/alcohols/background.html#top

The carbon bearing the OH group:

Primary - has one R group and two hydrogens

Secondary - has two R groups and one hydrogens

Tertiary - has three R groups

(c) Two types reaction of alcohols

Fission of the RO-H bond

Fission of the R-OH bond

Alcohols has tendency for H+ to dissociate in presence of a base

Alcohols act like acids [weaker acid than water]

(d) Fission of RO-H bondhttp://www.chemguide.co.uk/organicprops/alcohols/sodium.html#top(i) reaction with sodium ( H2(g) and Na alkoxide

ethanol + Na ( H2(g) + Na ethoxide

propanol + Na ( H2(g) + Na propoxide

(ii) reaction with carboxylic acid (esterifcation)

http://www.chemguide.co.uk/organicprops/alcohols/esterification.html#top propanol and butanoic acid ( propyl butanoate + water

butanol and propanoic acid ( butyl propanoate + water

Catalyst HCl or conc. H2SO4(e) Fission of the R-OH bond(i) Halogenation using: HCl, HBr, HI, PBr3, PCl5 [mention only]

(ii) Dehydration reaction with conc. H2SO4 (as catalyst)

http://www.chemguide.co.uk/organicprops/alcohols/dehydration.html#topA primary alcohol reacts with cold concentrated sulphuric acid to form alkyl hydrogensulphate :

Ethanol + conc. sulphuric acid ( Ethyl hydrogensulphate + Water

If the alcohol is in excess and the reaction mixture is warmed to 140oC, an ether is formedEthyl hydrogensulphate + ethanol (excess) ( Diethyl ether (ethoxyethane) +sulphuric acid

If the concentrated sulphuric is in excess and the temperature is raised to 170oC, water is eliminated, with the formation of an alkene:

ethyl hydrogensulphate + conc. sulphuric acid (excess) ( ethene + sulphuric acid

Dehydration mainly 3o alcohol carbocation stabilized by alkyl groups

(iii) oxidation

Combustion of 1o, 2o and 3o degradation of C skeleton ( CO2, H2O

Reaction with oxidants - maintain C skeletonReactions with: KMnO4 / H+; K2Cr2O7 / H+ Or Na2Cr2O7/ H+http://www.chemguide.co.uk/organicprops/alcohols/oxidation.html#top KMnO4/H+ is a stronger oxidizing agent than K2Cr2O7

Oxidation product depends on the class of alcohol

With K2Cr2O7 / H+ or Na2Cr2O7 / H+

1o oxidized to aldehydes and further oxidation to carboxylic acid if temperature is raised or if aldehyde is not distilled off

2o - oxidized to ketones

3o resistant to oxidation

With KMnO4/H+

1o oxidized directly to carboxylic acid

2o - oxidized to ketonesPrimary alcohol

Primary alcohol: -OH on C with 2 hydrogens attached [-OH on C attached to 1 other C]

During oxidation: [-2H] one from OH and one other

Result aldehyde

Aldehyde: 1 H attached to the carbonyl C

Further oxidation to the carboxylic acid

To obtain the aldehyde distill off as it is formed

Aldehyde has lower b.p. than alcohol no hydrogen bonds.

Primary alcohol ( aldehyde ( carboxylic acid

e.g. propan-1-ol, propanaldehyde, propanoic acid

Secondary alcohol

With KMnO4/H+, K2Cr2O7 / H+ or Na2Cr2O7 / H+

Secondary alcohol: -OH on C with 1 hydrogen attached

[-OH on C attached to 2 other C]

During oxidation: [-2H] one from OH and one other

Result ketone

The carbonyl carbon in a ketone does not have a hydrogen- no further oxidation (ketones resist oxidation)

Tertiary alcohol

Tertiary alcohol: -OH on C with 0 hydrogen attached

[-OH on C attached to 3 other C]

No oxidation except under extreme conditions

Iodoform reaction - (to be done again in aldehydes and ketones)

http://www.chemguide.co.uk/organicprops/alcohols/iodoform.html#top Alcohols with the formula CH3CH(OH)R [ethanol if R = H] are oxidized by sodium iodate (I) to CH3COR and therefore give a positive iodoform test.

In the formula CH3CH(OH)R: The alpha carbon is CH3. The alpha carbon is one carbon away from the carbon with the functional group.

Iodoform is CHI3: Tri-iodomethane (fine yellow crystals with characteristic smell)Stage 1: alcohol is oxidized to a carbonyl compound

Example: Ethanol in the presence of I2 / NaOH ( Ethanal

Stage 2: The 3 hydrogens on the alpha carbon are replaced with iodineExample: ethanal in the presence of I2 / NaOH ( Tri-iodo-ethanalStage 3: The excess base hydrolyses the molecule and causes the C-C bond to break, releasing triiodomethane [CHI3].

Example: Tri-iodo-ethanal in the presence of OH- ( Tri-iodomethane + the methoxide anion

From Chemguide:

Summary of the reactions during the triiodomethane (iodoform) reaction

We will take the reagents as being iodine and sodium hydroxide solution.

(e) The structure of phenol

http://www.chemguide.co.uk/organicprops/phenol/background.html#top Phenol will be look at again after the topic BENZENE

From Chemguide:

The structure of phenolThe simplest way to draw the structure of phenol is:

There is an interaction between the delocalised electrons in the benzene ring and one of the lone pairs on the oxygen atom. This has an important effect on both the properties of the ring and of the -OH group.

One of the lone pairs on the oxygen overlaps with the delocalised ring electron system . . .

. . . giving a structure rather like this:

The donation of the oxygen's lone pair into the ring system increases the electron density around the ring. That makes the ring much more reactive than it is in benzene itself.

It also helps to make the -OH group's hydrogen a lot more acidic than it is in alcohols.

The -OH group attached to the benzene ring in phenol has the effect of making the ring much more reactive than it would otherwise be.

For example, as you will find below, phenol will react with a solution of bromine in water (bromine water) in the cold and in the absence of any catalyst. It also reacts with dilute nitric acid, whereas benzene itself needs a nitrating mixture of concentrated nitric acid and concentrated sulphuric acid.

Reaction with bromine water

http://www.chemguide.co.uk/organicprops/phenol/ring.html#top If bromine water is added to a solution of phenol in water, the bromine water is decolourised and a white precipitate is formed which smells of antiseptic.

The precipitate is 2,4,6-tribromophenol.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/maketbp.gif" \* MERGEFORMATINET Notice the multiple substitution around the ring - into all the activated positions. (The 6- position is, of course, just the same as the 2- position. Both are next door to the -OH group.)

Note: Bromine water is normally used as a test for a C=C double bond. The important difference with phenol is the formation of a white precipitate as well as the bromine water being decolourised.

If you choose to follow this link, use the BACK button on your browser to return to this page.Combustion of phenol

http://www.chemguide.co.uk/organicprops/phenol/other.html#top

Phenol burns in a plentiful supply of oxygen to give carbon dioxide and water.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/burnphenol.gif" \* MERGEFORMATINET However, for compounds containing benzene rings, combustion is hardly ever complete, especially if they are burnt in air. The high proportion of carbon in phenol means that you need a very high proportion of oxygen to phenol to get complete combustion. Look at the equation.

As a general rule, the hydrogen in a molecule tends to get what oxygen is available first, leaving the carbon to form carbon itself, or carbon monoxide, if there isn't enough oxygen to go round.

Phenol tends to burn in air with an extremely smoky flame - full of carbon particles.

Esterification of phenol

http://www.chemguide.co.uk/organicprops/phenol/other.html#top

You will probably remember that you can make esters from alcohols by reacting them with carboxylic acids. You might expect phenol to be similar.

However, unlike alcohols, phenol reacts so slowly with carboxylic acids that you normally react it with acyl chlorides (acid chlorides) or acid anhydrides instead.

Making esters from phenol using an acyl chlorideA typical acyl chloride is ethanoyl chloride, CH3COCl.

Phenol reacts with ethanoyl chloride at room temperature, although the reaction isn't as fast as the one between ethanoyl chloride and an alcohol. Phenyl ethanoate is formed together with hydrogen chloride gas.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/phenetheqn1.gif" \* MERGEFORMATINET Sometimes it is necessary to modify the phenol first to make the reaction faster.

For example, benzoyl chloride has the formula C6H5COCl. The -COCl group is attached directly to a benzene ring. It is much less reactive than simple acyl chlorides like ethanoyl chloride.

In order to get a reasonably quick reaction with benzoyl chloride, the phenol is first converted into sodium phenoxide by dissolving it in sodium hydroxide solution.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/makenaphen.gif" \* MERGEFORMATINET The phenoxide ion reacts more rapidly with benzoyl chloride than the original phenol does, but even so you have to shake it with benzoyl chloride for about 15 minutes. Solid phenyl benzoate is formed.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/phenbenzeqn.gif" \* MERGEFORMATINET Making esters from phenol using an acid anhydrideA typical acid anhydride is ethanoic anhydride, (CH3CO)2O.

The reactions of acid anhydrides are slower than the corresponding reactions with acyl chlorides, and you usually need to warm the mixture.

Again, you can react the phenol with sodium hydroxide solution first, producing the more reactive phenoxide ion.

If you simply use phenol and ethanoic anhydride, phenyl ethanoate is formed together with ethanoic acid.

This reaction isn't important itself, but a very similar reaction is involved in the manufacture of aspirin (covered in detail on another page - link below).

If the phenol is first converted into sodium phenoxide by adding sodium hydroxide solution, the reaction is faster. Phenyl ethanoate is again formed, but this time the other product is sodium ethanoate rather than ethanoic acid.

Properties of phenol as an acid

http://www.chemguide.co.uk/organicprops/phenol/acidity.html#top

With indicatorsThe pH of a typical dilute solution of phenol in water is likely to be around 5 - 6 (depending on its concentration). That means that a very dilute solution isn't really acidic enough to turn litmus paper fully red. Litmus paper is blue at pH 8 and red at pH 5. Anything in between is going to show as some shade of "neutral".

With sodium hydroxide solutionPhenol reacts with sodium hydroxide solution to give a colourless solution containing sodium phenoxide.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/phenolnaoh.gif" \* MERGEFORMATINET In this reaction, the hydrogen ion has been removed by the strongly basic hydroxide ion in the sodium hydroxide solution.

With sodium carbonate or sodium hydrogencarbonatePhenol isn't acidic enough to react with either of these. Or, looked at another way, the carbonate and hydrogencarbonate ions aren't strong enough bases to take a hydrogen ion from the phenol.

Unlike the majority of acids, phenol doesn't give carbon dioxide when you mix it with one of these.

This lack of reaction is actually useful. You can recognise phenol because:

It is fairly insoluble in water.

It reacts with sodium hydroxide solution to give a colourless solution (and therefore must be acidic).

It doesn't react with sodium carbonate or hydrogencarbonate solutions (and so must be only very weakly acidic).

With metallic sodiumAcids react with the more reactive metals to give hydrogen gas. Phenol is no exception - the only difference is the slow reaction because phenol is such a weak acid.

Phenol is warmed in a dry tube until it is molten, and a small piece of sodium added. There is some fizzing as hydrogen gas is given off. The mixture left in the tube will contain sodium phenoxide.

INCLUDEPICTURE "http://www.chemguide.co.uk/organicprops/phenol/phenolna.gif" \* MERGEFORMATINET CAMPION J. MARSHALL CAPE CHEM U2 M1 ORGANIC ALCOHOLS & PHENOL PAGE 1 OF 9