CHEMISTRY FORM 5 ORGANIC CHEMISTRY-ALCOHOL AND PHENOL
CHEMISTRY FORM 5 ORGANIC CHEMISTRY-ALCOHOL AND PHENOL
ALCOHOL AND PHENOL
- These are organic compounds with hydroxyl group as functional group.
- Alcohols and phenol are formed when at least one hydrogen atom of hydrocarbons is replaced by hydroxyl group.
- When the hydrogen atom is replaced from aliphatic hydrocarbon the resulting compound is known as alcohol.
- When the hydrogen atom is replaced from benzene then the resulting compound is known as phenol.
- Most of properties of alcohol resembles with those of phenol due to similarity in their functional group but some properties are different due to difference in their structure.
CLASSIFICATION OF ALCOHOLS
- Like in haloalkanes, according to number of alkyl groups which are directly bonded to a carbon , alcohols can be classified into three categories.
i. Primary (10) alcohols
ii. Secondary (20) alcohols
iii. Tertiary (30) alcohols
i. PRIMARY (10) ALCOHOLS
- These are alcohols where by a carbon with hydroxyl group is also directly bonded to one alkyl group only.
- Thus far alcohols with one hydroxyl group, the carbon with is also directly bonded to two hydrogen atoms.
i.e. where alkyl group only
ii. SECONDARY (20) ALCOHOLS
- These are alcohols where by a carbon with hydroxyl group is also directly bonded to two alkyl groups.
– Thus for alcohol with one hydroxyl group, the carbon with is also directly bonded to one hydrogen atom only.
iii. TERTIARY (30 ) ALCOHOL
- These are alcohols where by a carbon with hydroxyl group is also directly bonded to three alkyl groups.
– Thus there is no hydrogen which is directly bonded to the carbon with .
NOMENCLATURE OF ALCOHOLS
• Rules of naming alcohols are the same as those alkanes with the following modifications
i. The parent chain must contain hydroxyl group
ii. In numbering carbons start at the end closer to hydroxyl group.
iii. Position of hydroxyl group should be indicated by using Arabic numerals.
iv. In giving a name of alcohol, the name must end with suffix ol ( after removing e from corresponding name of hydrocarbon)
Give systematic (IUPAC) name of the following organic compounds.
4 – Cyclopropyl- 2 tertbutylpentanol.
OR ( 4- Cyclopropyl – 2- terbuty-pentan-1-ol
Pent – 3 con 1- 01
OR (3 – pentanol).
Pent – 3 – yn – 2- ol.
1 – Pheny methanol.
2,3 – dihydroxyl phenol OR (1,2,3,- trihydroxylbenzene)
2 – nitrophenol.
PREPARATION OF ALCOHOLS
a) REACTION BETWEEN MOIST SILVER OXIDE AN HALOALKANE.
b) REACTION BETWEEN HALOALKANE AND ALKALINE SOLUTION.
• Haloalkane react with alkaline solution like NaOH and KOH yielding alcohol
E.g. In case of NaOH
c) ACIDIC HYDROLYSIS OF ALKENE ( REACTION BETWEEN ALKENE AND WATER UNDER PRESENCE OF SULPHURIC ACID).
d) REDUCTION OF CARBONYL COMPOUNDS
• Carbonyl compounds react with reducing agent like alcohols.
• Aldehydes give primary alcohol.
• Ketones give secondary alcohol.
e) REDUCTION OF CARBOXYLIC ACID
• Carboxylic acids react with strong reducing agent like forming primary alcohols.
In above reaction if is in limited amount ( or weak reducing agent is used instead of ) aldehyde is formed instead of alcohol.
f) REACTION BETWEEN GRIGINARD REAGENT AND CARBOXYLIC COMPOUNDS ACID FOLLOWED BY ACIDIC HYDROLYSIS
• If the aldehyde used is methanol, primary alcohol is formed.
• If higher member of aldehyde is used, secondary alcohol is formed.
• If the carbonyl compound which is used is Ketone, tertiary alcohol is formed.
PHYSICAL PROPERTIES OF ALCOHOLS
• Boiling point of alcohol increase with an increase of number of carbon ( As number of carbon increase the molecular weight also increase)
Boiling point of is large than the
– The less branched alcohol has higher boiling point than that alcohol which is more branched.
– The more branched has lower boiling point due to the following reason,
i. Poor package of carbon atoms
ii. Minimum surface area as it attain more spherical shape hence heating become easier
-In comparison to alcohol and corresponding carbon member of alkene ( with approximately the same molecular weight) alcohol have higher boiling due to presence of hydrogen bond in alcohol.
– For polyhydric alcohols. Alcohol with more than one OH– group has the boiling point increase, with number of hydroxyl groups due to increase in position of making hydrogen bond.
Explain the following the B.P ( boiling point) of ethyl glycol is highest among the compound given below although is little in the molecular weight.
|compound||Formula||Molecular weight||Boiling point in oc|
Boiling point of alcohol increase with an increase in number of group.
(for polyhydric alcohol) due to increase in number of position of making hydrogen bonding, ethylene glycol has two groups so compare to 1- propanol which has only one group. Ethylene glycol, have many position of making hydrogen bonding and hence the boiling will be higher, in case of butane it has group, there is no hydrogen bonding at all that is why has lowest boiling point compound.
Solubility of alcohol in water decrease with an increase hydrophobic group ( increase number of carbons due to an increase of non polar covalent character).
In increase of polyhydric alcohols solubility increase with an increase in number of group as a result of increasing number of position of making hydrogen bonding.
Example. NECTA 1993 PP1
Explain the solubility of alcohol increase with order
For Polyhydric alcohol solubility increase with an increase in number of position of making hydrogen bonding that is why solubility of given compound increase in that order (i.e the longer the number of group the higher the solubility will be).Alcohol exist as coloured liquid compound because hence easily exposed
EXPLANATION ON COMPARISON OF ACIDIC STRENGTH IN ALCOHOLS AND PHENOLS
Phenol is stronger acid than alcohol due to following reason
1. Easier of releasing hydrogen proton
2. Stability of phenoxide ion formed after releasing hydrogen proton
1. EASIER OF RELEASING HYDROGEN ATOM
Lone pair electrons in oxygen of groups in phenol are localized they are involved in mesomerism (+M) i.e they are delocalized.
The delocalization of lone pair electron tends to form +ve charge in oxygen atom of group thus making easier to releasing oxygen proton.
There is no such occasion in alcohol
2. STABILITY OF PHENOXIDE ION FORMED AFTER RELEASING HYDROGEN PROTON
From above mechanism in phenoxide ion, it clearly understood negative charged electrons in oxygen atom of phenoxide is delocalized thus stabilizing the negative charge formed releasing hydrogen proton i.e ( it can exist on its own with combining with hydrogen proton). There is no such occusion alcoxide ion RO– formed in alcohol after releasing hydrogen proton.
ACIDIC THAN ALCOHOL
A. a) REACTION WITH ALKALINE SOLUTION
With alkaline solution like NaOH phenol tend to react with them
Example with phenol form sodium phenoxide.
There is no such reaction with alcohol indicating that alcohol has basic character and hence phenol is more acidic than alcohol
Alcohol+ alkaline solution No reaction
The reaction is very important in separating phenol from other class of alcohol.
Qn. Without using the distillation explain how would you separate the following pair of organic compounds
i. Phenol and 1- hexanol
ii. Phenol and benzene
b) REACTION WITH SODIUM CARBONATE
Acids react with carbonate to form carbon dioxide gas phenol like other acids react with sodium carbonate to evolve a gas.
Phenol like other acid react with sodium carbonate evolve a gas which turns lime water milky.
c) REACTION WITH CARBOXYLIC ACID
Alcohol react with carboxylic acid in presence of sulphuric to form ester and water.
This verify that alcohol has basic character in this case phenol it does not react with carboxylic acid either in presence or in absence of suplhuric acid. This verify that phenol some alcohol character and hence phenol has higher strength than alcohol.
CHEMISTRY FORM 5 ORGANIC CHEMISTRY-ALCOHOL AND PHENOL
CHEMICAL REACTION OF ALCOHOL
Ø Chemical reaction of alcohol can be classified into the following
a. Reaction which involve replacement of whole OH– group
b. Reactions which involve replacement of H from OH– group
c. Reactions which involve OH– group and β- hydrogen
A. REACTION WHICH INVOLVE REPLACEMENT OF HYDROGEN ATOM
Ø Under this heading alcohol react with strong alkaline metals like Li, Na, K to form alkoxide and hydrogen gas is
Ø The main reaction under this heading is halogenations of alcohol.
involved in the above reaction produce denser white fumes with ammonia so that reaction is used as test of presence of group in the compound.
B. REACTION WHICH INVOLVE OH– GROUP AND B- HYDROGEN.
Under this heading alcohol undergo elimination reaction to from alkene.
The production of either in above reaction is more favoured when is dilute and cold.
Ø With weak oxidation agent like primary alcohol tend to form aldehyde.
With strong oxidizing agent like carboxylic acid is formed.
-With either weak oxidizing or strong oxiding agent secondary alcohol from Ketone.
Tertiary alcohol remit oxidation since there is no hydrogen to be removed.
Ø This is the chemical test for presence of terminal methyl group which is directly bonded to carbon with OH– group or (to carbonyl group in the case of carbonyl compounds) by giving yellow ppt of trichloromethane ( Iodoform) CHI3.
Ø When compounds with terminal methyl group bonded to carbon with OH group is heated with 12 in presence of NaOH they give yellow ppt of Iodoform.
CHEMICAL TEST TO DISTINGUISH BETWEEN PRIMARY, SECONDARY AND TERTIARY ALCOHOLS.
– Three classes of alcohol can be distinguished by using Lucas reagent.
– Lucas reagent is the mixture of concentrated HCl and ZnCl mixed at equal proportion.
– With Lucas reagent at room temperature, primary alcohol do not form cloudness or turbidity( insoluble substance) at all.
– Secondary alcohol tends to form turbidity ( insoluble substance which is chloroalkane within 5 minutes).
– Tertiary alcohol, tend to form turbidity immediately.
Qn. Gave chemical test to distinguish between
i. Ethanol and propanol ( I test)
ii. Butan – 1-ol and butan – 2- ol (2 test)
iii. Butan -2- ol and 2- methyl propan – 2-ol ( 2 test apart from using Lucas reagent)
i. Ethanol gives positive Iodoform test while propanol give negative Iodoform test.
ii. 1st TEST
With Lucas reagent at room temperature butan -2-ol give turbidity ( cloudness) within 5 minutes while butan -1-ol do not give turbidity at all.
2nd TEST ( Iodoform Test)
Butan -2- ol give positive iodoform test while but-1-ol give negative iodoform test.
When butan -2- ol is mixed with solution the orange colour of is changed to green while 2- methylpropan- 2 – ol do not show any change.
Butan decolourise KMnO4 with black ppt appearing at the bottom of the beaker which is deep purple while 2-methylpropan do not.
NECTA 2006 PP2 QN. 8(a)
Organic compound C4H10O reacts with PCl5 to form an organic compound “Q” In organic compound “N” and gas ‘R’ which produce denser white fumes with a aqueous ammonia “P” also react with a mixture of Iodine and NaOH forming a sodium salt “W” and triodomethane.
i. Identify and write the structural formula Q, R and W.
ii. Write an equation of each of the above reaction.
The molecular formula confirm general molecular formula of CnH2n+2O
– Thus P is either alcohol or ether.
– A gas which produce dense white fumes with aquous ammonia is HCl
– So since the reaction “P” and PCl5 produce HCl then there is OH group in P.
– Hence compound “P” reacts with mixture of iodine and NaOH to give triodemethane then compound “P” give positive Iodoform.
– Hence in “P” there is terminal methyl groups bonded to carbon with group. This “P” is butan -2-ol.
Its structure is
– Q is 2 – chlorobutane
– Its structure is
– N is PoCl3
– R is HCl
– W – is sodium propanoate
– Its structure is
CHEMICAL REACTIONS OF PHENOL
Generally chemical reactions of phenol can be divided into two types;
i. Electrophilic substitution reactions inside OH– group.
ii. Electrophilic substitution reactions in benzene ring.
1. ELECTROPHILIC SUBSTITUTION REACTION INSIDE OH– GROUP
a) REACTION WITH ALKALINE SOLUTION
Unlike Alcohol, phenol react with alkaline soluble NaOH
i.e. Alcohol + Alkaline solution. e.g, No reaction
The reactions give one of the differences between alcohol and phenol
b) REACTION WITH ALKALING METALS
Phenol reacts, with alkaline metals like etc to form phenoxide and hydrogen gas is involved.
The reaction show one of the similarities between alcohol and phenol.
Alcohol + alkaline metal Allcoxide + Hydrogen gas.
c) FORMATION OF ETHER
Phenol react with haloalkane in presence of acqueous sodium hydroxide to form ether.
The reaction show another similarity between alcohol and phenol although in alcohol there is no need of .
d) FORMATION OF ESTER
Phenol reacts with acyl compounds in presence of NaO to form ester.
and phenol i.e alcohol also reacts with acyl compounds to form ester although in alcohol there is no need of NaOH(aq).
e) REACTION WITH SODIUM CARBONATE.
Phenol reacts with sodium carbonate to form phenoxide and the gas which turn lime water milky i.e. CO2 gas is evolved.
– The reaction show another difference between alcohol and phenol i.e. Alcohol reacts with .
II. ELECTROPHILIC SUBSTITUTION REACTION IN BENZENE RING
– Under this heading phenol reacts like benzene the only difference is that OH– group in phenol directs incoming electrophile at ortho and Para position.
TESTS OF PHENOL
Phenol turns blue litmus paper into red
– With ion (III) Chloride phenol tends to form purple violet color of ion(III) phenoxide.
– With bromine water phenols tend to form white ppt of 2-tribomophenol.
SOME DIFFERENCES BETWEEN ALCOHOL AND PHENOL
|1.||Undergo oxidation easily ( for primary and secondary alcohol)
|Do not undergo oxidation easily|
|2||Do not react with bromine water
|Form white ppt of 2, 4, 6 – tribomophenol with bromine water.|
|3||Do not react with FeCl3
|Form purple colouration with ion(III) chloride.|
|4||Form ester ( has fruity smell)
|Do not react with carboxylic acid|
|5||Do not react with sodium hydroxide solution
|Form white ppt of sodium phenoxide with NaOH(aq).|
|6||Do not react with sodium carbonate
|Form white ppt of sodium phenoxide and gas which turns lime water milky (i.e CO2 is evolved).
SIMILARITIES BETWEEN ALCOHOL AND PHENOL
– Evolve hydrogen gas with alkaline metals.
– They form ether with haloalkane.
– They form ester with acyl compound.
– They reacts with hydrogen halide.