1. Alcohols and Phenols By Dr. Nahed Nasser

2. CONTENTS Structure of alcohols Types of alcohols Classification of alcohols Nomenclature of alcohols Hydrogen bonding and acidity )Physical properties) Structure of phenols Nomenclature of phenols Preparation of alcohols Preparation of phenols Reactions of alcohols Reactions of phenols Uses of alcohols and phenols THE CHEMISTRY OF ALCOHOLS and PHENOLS 2

3. STRUCTURE OF ALCOHOLS Alcohols are the family of compounds that contain one or more hydroxyl (-OH) groups. The OH group is bound to a carbon atom. They can be considered both derivatives of hydrocarbons (by replacing a hydrogen atom with a hydroxyl group -OH) and water (H 2 O) derivatives (the result of the substitution of a hydrogen atom by an organic radical). TYPES OF ALCOHOLS Two types of alcohols Two types of alcohols : mono hydroxyls (for example ethanol C 2 H 5 OH) and poly hydroxyls (for example: propantriol CH 2 OH-CHOH-CH 2 OH). The alcohols containing 2 hydroxyl groups connected by different carbon atoms are called glycols, for example: Ethylene glycol CH 2 OH-CH 2 OH. Classification of Monohydroxyl Alcohols The mono hydroxyl alcohols can be classified into three types according to the type of the carbon atom connected to the hydroxyl group: - primary alcohols - secondary alcohols - tertiary alcohols PRIMARY 1° SECONDARY 2° TERTIARY 3° 3

4. For example, methanol CH 3 OH, ethanol CH 3 -CH 2 -OH, allyl acohol CH 2 =CHCH 2 OH are primary alcohols; 2-propanol CH 3 -CH(OH)-CH 3 is a secondary alcohol and 2-methyl- 2-propanol CH 3 -C(CH 3 )OH-CH 3 is a tertiary alcohol. 4

5. COMMON NOMENCLATURE OF ALCOHOLS Alcohols are named as alkyl alcohols i.e. name the alkyl group and follow it by the word alcohol CH 3 OH CH 3 CH 2 OH CH 2 =CHCH 2 OH Common names Methyl alcohol Ethyl alcohol Allyl alcohol NOMENCLATURE OF ALCOHOLS The alcohols containing 2 hydroxyl groups (diols) connected to two different carbons are called glycols for example: CH 2 OH-CH 2 OH is called ethylene gylcol CH 3 -CH(OH)-CH 2 (OH) is called propylene gylcol Isopropyl alcohol Cyclopentyl alcohol Methylcyclohexyl alcohol 5

6. IUPAC NOMENCLATURE OF ALCOHOLS Find the longest chain of C atoms containing the O-H group; to obtain the name of the parent alkane Replace the e ending by ol suffix in the basic name Number the chain starting from the end nearer to the O-H group and add a locator number for OH group just before the ol suffix or before the full name e.g. CH 3 CH(OH)CH 2 CH 3 is named 2 -butanol or butan-2-ol Identify the substituents, allocate them numbers, then list them in alphabetical order. Examples: CH 3 - CH(CH 3 ) - CH 2 - CH 2 - CH(OH) - CH 3 is named 5-methylhexan-2-ol 6 5 4 3 2 1 or 5-methyl-2-hexanol 6

7. ( CH 3 ) 2 C=CHCH(OH)CH 3 is 4-methyl-3-penten-2-ol. 5 4 3 2 1 If a molecule contains both an OH group and a c=c or c=c bond, the name should include suffixes indicate presence of both OH group and the unsaturated groups. The OH group takes preference before the double or triple bonds in getting the lower number. 7

8. If the parent hydrocarbon contain two hydroxyl groups, the suffix diol is added to the name; the suffix triol is added when there are three OH groups. In each case the relative positions of OH groups must be identified. 8

9. 9 STRUCTURE OF PHENOL C6 H6 O Phenol’s chemical formula is C6H5OH, it has the OH group directly attached to the benzene ring. Thus the following compounds are alcohols not phenols

10. Nomenclature of phenols Phenols are generally named as derivatives of the simplest member of the family, phenol. Either the ortho, meta, para system or the numbering system can be employed. Numbering of the ring begins at the hydroxyl-substituted carbon and proceeds in the direction of the next substituted carbon that possesses the lower number. Some phenols have common names: 10

11. Physical Properties of Alcohols Boiling Points of Alcohols Alcohols have higher boiling points than alkanes of similar mass This is due to the presence of inter-molecular hydrogen bonding that connect alcohol molecules together thus more energy is required to separate the molecules. hydrogen bonding M r bp / °C propaneC 3 H 8 44 -42 ethanolC 2 H 5 OH 46 +78 The boiling points increases with increase in molecular weights 11

12. Boiling point is higher for straight chain isomers i.e. branching decrease the boiling points bp / °C butan-1-ol CH 3 CH 2 CH 2 CH 2 OH118 butan-2-ol CH 3 CH 2 CH(OH)CH 3 100 2-methylpropan-2-ol (CH 3 ) 3 COH 83 Greater branching = lower inter-molecular forces (H-B) = lower boiling points 12

13. Solubility Of Alcohols Low molecular mass alcohols are miscible with water Due to hydrogen bonding between the two molecules Heavier alcohols are less miscible i.e. As the number of carbon atoms increase the miscibility decrease As the number of OH groups present in a molecule increase the miscibility increase. Thus triols > diols > monohydroxyl alcohols in solubility in water Acidic properties of alcohols: Alcohols are very weak acids thus they don’t react with bases 13

14. Phenol is a crystalline solid, with a higher boiling point than alcohols, and it is moderately soluble in water. Compared to aliphatic alcohols phenolmuch higher acidityIt is slightly acidic: the phenol molecule has weak tendencies to lose the H + ion from the hydroxyl group, resulting in the highly water-soluble phenolate anion C 6 H 5 O −, called phenoxide anion. Compared to aliphatic alcohols, phenol shows much higher acidity (about 1 million times more acidic) resonance stabilization orthoparaOne explanation for the increased acidity over alcohols is resonance stabilization of the phenoxide anion by the aromatic ring. In this way, the negative charge on oxygen is shared by the ortho and para carbon atoms. Physical Properties of Phenols

15. 15 While introduction of electron releasing groups (e.g. OR, R) decrease the acidity of phenols compared to unsubstituted phenol. Introduction of electron withdrawing groups such as NO 2 or CN on the benzene ring increases the acidity of phenols, While introduction of electron releasing groups (e.g. OR, R) decrease the acidity of phenols compared to unsubstituted phenol. thus: Phenols are less acidic than carboxylic acids Phenols are less acidic than carboxylic acids

16. Preparation of Alcohols 1- From alkenes

17. 2- From alkyl halide by nucleophilic substitution 3- By reduction of aldehydes, ketones and carboxylic acids using metal hydrides

18. 4- By nucleophilic addition of Grignard reagent to aldehydes, ketones and esters Addition of RMgX to formaldehyde gives 1 ◦ alc. Addition of RMgX to any other aldehyde gives 2 ◦ alc. Addition of RMgX to ketones and esters give 3 ◦ alc.

19. Preparation of Phenols 1- Via hydrolysis of Diazonium salts 2- Fusion of sodium with benzene-sulfonates: 3- From alkyl halide:

20. Typical Alcohol Reactions Typical Alcohol Reactions Salt formation Dehydration ( Alkene and ether formation) Ester formation Alkyl halide formation Oxidation Typical Phenol Reactions Typical Phenol Reactions Salt formation Oxidation Reactions of aromatic ring and side chain of phenols 20

21. Reaction of Alcohols and Phenols 1- Salt Formation by reaction with active metal

22. 2- ELIMINATION OF WATER (DEHYDRATION) Reagent/catalyst conc. sulphuric acid (H 2 SO 4 ) or conc. phosphoric acid (H 3 PO 4 ) Conditions reflux at 180°C Product alkene While dehydration of alcohols at lower temperature will give ethers

23. 3- Ester formation carboxylic acid + alcohol in presence of strong acid catalyst (e.g conc. H 2 SO 4 ) produces esters 23 4- Alkyl halides formation

24. 5- OXIDATION OF ALCOHOLS Alcohols can be oxidised depending on their class Oxidation is used to differentiate between primary, secondary and tertiary alcohols The usual reagent is acidified potassium dichromate(VI) PrimaryEasily oxidised to aldehydes and then to carboxylic acids. e.g. CH 3 CH 2 OH(l) + [O] ——> CH 3 CHO(l) + H 2 O(l) ethanol ethanal it is essential to distil off the aldehyde before it gets oxidised to the acid CH 3 CHO(l) + [O] ——> CH 3 COOH(l) ethanal ethanoic acid SecondaryEasily oxidised to ketones TertiaryNot oxidised under normal conditions. They do break down with very vigorous oxidation PRIMARY 1° SECONDARY 2° TERTIARY 3° 24

25. Why 1 ° and 2° alcohols are easily oxidised and 3 ° alcohols are not For oxidation to take place easily you must have two hydrogen atoms on adjacent C and O atoms. H H R C O + [O] R C O + H 2 O HH R C O + [O] R C O + H 2 O RR R H R C O + [O] R This is possible in 1° and 2° alcohols but not in 3° alcohols. 1°1° 2°2° 3°3° 25

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27. Reactions of aromatic ring of phenols

28. USES OF ALCOHOLS AND PHENOLS Uses of Alcohols Methanol and ethanol can be used as an alternative to fossil fuels as they burn very cleanly, producing only carbon dioxide and water. Ethanol is considered a renewable fuel as it can be made from renewable sources such a sugar cane and can be used as a fuel in its own right, or in mixtures with petrol (gasoline). It's really useful for countries without an oil industry as it reduces their dependence upon imports of petrol. As ethanol is the least toxic of the alcohols it is used in perfumes to stop the plant and animal extracts from going off. The amount added depends on whether you are making a perfume, toilet water or cologne. As ethanol is the safest of the alcohols it is often used to dissolve chemicals that are insoluble in water. Examples include perfumes, cosmetics and vegetable essences such as vanilla extract. Methylated spirits which is ethanol with a small quantity of methanol added (The methanol makes the mixture highly poisonous ) is very good for cleaning paint brushes. Glycerol used in midicine. Uses of phenol It is used in an air freshener Another use for phenol includes an intermediate stage in the process of producing caprolactam, which is used in nylon and many other man-made fibres. Phenol is also a powerful disinfectant and bacteria killer. However the chemical is highly corrosive and moderately toxic. It effects humans by burning the skin and other tissue that it comes into contact with. This gives severe skin burning and if inhaled serious internal corrosion. The skin burning is not initially felt because the phenol has a local anaesthetic effect. It can affect the central nervous system, which will at first lead to sweating, weakness, dizziness and twitching but with prolonged exposure leads to nausea, vomiting and coma. If ingested even a small dose can lead to be fatal in humans and therefore care must be taken at all times using phenol-containing products. Resorcinol is used in mouth wash 28