1. Fall, 2013 Dr Seemal Jelani Chem-240 1

2.  Nomenclature  Properties  Preparation  Reaction Spring, 2011 Dr Seemal Jelani Chem-240 2

3.  Considered derivatives of water Spring, 2011 Dr Seemal Jelani Chem-240 3

4.  Pure phenol is a white crystalline solid, smelling of disinfectant  It has to be handled with great care because it causes immediate white blistering to the skin  The crystals are often rather wet and discolored. Spring, 2011 Dr Seemal Jelani Chem-240 4

5.  The simple monohydric phenols are either liquid with low melting crystalline  Some chromophoric group is present in their molecules but phenols are generally colorless Spring, 2011 Dr Seemal Jelani Chem-240 5

6.  What is the reason of coloration in phenols The colour of many phenols may be due to the presence of chromophoric group and also due to the presence of their oxidation products as impurities because they are easily oxidized on exposure to air Spring, 2011 Dr Seemal Jelani Chem-240 6

7.  It is useful to compare phenol's melting and boiling points with those of methylbenzene (toluene)  Both molecules contain the same number of electrons and are a very similar shape  That means that the intermolecular attractions due to Vander Waals dispersion forces are going to be very similar. Spring, 2011 Dr Seemal Jelani Chem-240 7

8.  The symmetrical phenols generally have higher MP than unsymmetrical isomers  Examples  Among the chlorophenols, the para isomer has the highest MP, whereas the ortho isomer is liquid at ordinary temperature Spring, 2011 Dr Seemal Jelani Chem-240 8

9. C 6 H 5 OH C 6 H 5 CH 3 Melting point (°C) 40-43 °C -95 °C C)Boiling point (°C) 118 °C 111 °C Spring, 2011 Dr Seemal Jelani Chem-240 9

10.  The reason for the higher values for phenol is in partly due to permanent dipole-dipole attractions due to the electronegativity of the oxygen - but is mainly due to hydrogen bonding.  Hydrogen bonds can form between a lone pair on an oxygen on one molecule and the hydrogen on the - OH group of one of its neighbors. Spring, 2011 Dr Seemal Jelani Chem-240 10

11.  The O-H bond of phenols is more polar than that of alcohols  Phenols therefore form stronger HB than alcohols, resulting in higher BP and greater solubility in water  Compare the boiling point and solubility of phenol with that of Cyclohexanol ( a comparable alcohol) Spring, 2011 Dr Seemal Jelani Chem-240 11

12.  Cyclohexanol boils at 161 degree C and has solubility of 3.6g/100 mL of water  According to the general rule, symmetrical molecules should have lower boiling points than the unsymmetrical molecules. This is not the case with phenols, particularly those having an electronegative substituent ortho to the -OH group Spring, 2011 Dr Seemal Jelani Chem-240 12

13.  Because it has been seen that in many such cases the ortho isomers, despite their lack of symmetry, have BP much lower than the meta and para isomers  Compare the BP of o and p nitrophenols The lower BP ( higher volatility) of o- nitrophenol can be attributed to intramolecular HB ( chelation) Spring, 2011 Dr Seemal Jelani Chem-240 13

14.  Chelation of o-nitrophenol helps its separation from its m- and p isomers by steam distillation  Non- chelated m- and p- nitrophenols are not steam- volatile due to the intermolecular HB which inhibits their steam-volatility by lowering their vapour pressure Spring, 2011 Dr Seemal Jelani Chem-240 14

15.  Phenol is moderately soluble in water - about 8 g of phenol will dissolve in 100 g of water.  If you try to dissolve more than this, you get two layers of liquid. The top layer is a solution of phenol in water, and the bottom one a solution of water in phenol Spring, 2011 Dr Seemal Jelani Chem-240 15

16.  Solubility of phenols increases with an increase in the number of –OH which cause increased hydrogen bonding  However this effect is counterbalance by the symmetry of the molecules which helps them to stabilize by themselves Spring, 2011 Dr Seemal Jelani Chem-240 16

17.  Example Resorcinol has solubility of 123g/100 mL of water at 25 0 C, hydroquinone is soluble only to the extent of 8g/100 mL of water 25 0 C Spring, 2011 Dr Seemal Jelani Chem-240 17

18. Spring, 2011 Dr Seemal Jelani Chem-240 18

19.  Water is soluble in phenol to the extent of 29 g /100 mL of phenol  Phenols and water are miscible in all proportions above 65 0 C  A small amount of water lowers the MP of phenols, thus phenol which has the MP of 42 0 C often found as semi liquid because of the presence of small amount of water; it is completely liquified by the addition of about 5% of water Spring, 2011 Dr Seemal Jelani Chem-240 19

20.  The liquid form of phenol, containing 5% of water is known as Carbolic acid and it is used as disinfectant and germicide Spring, 2011 Dr Seemal Jelani Chem-240 20

21.  The solubility behaviour of phenol and water is complicated  Phenol is somewhat soluble in water because of its ability to form hydrogen bonds with the water. Spring, 2011 Dr Seemal Jelani Chem-240 21

22.  Common natural source – coal tar  Found in many plants Spring, 2011 Dr Seemal Jelani Chem-240 22

23. Spring, 2011 Dr Seemal Jelani Chem-240 23

24.  Hydroxybenzene is used as a parent name in most of its derivatives  Name substituents on aromatic ring by their position from OH Spring, 2011 Dr Seemal Jelani Chem-240 24

25.  While naming the polyfunctional aromatic compounds the hydroxy function is generally placed low in the order of priority  Only amino and ether functions are placed lower than the hydroxy function  Examples: p-hydroxy benzoic acid p-Amino phenol Spring, 2011 Dr Seemal Jelani Chem-240 25

26.  Many common names in use Spring, 2011 Dr Seemal Jelani Chem-240 26

27.  Ar-OH is more acidic than ROH  Soluble in dilute NaOH  Anion is resonance stabilized  EWG make phenols more acidic than phenol  EDG make phenols less acidic than phenol Spring, 2011 Dr Seemal Jelani Chem-240 27

28.  Although phenols and alcohols have the same FG –OH, phenols are much more acidic than alcohols but weaker acids than carboxylic acids  The pK a values of alcohols, phenols and carboxylic acids are in the vicinity of 18,10 and 5 Spring, 2011 Dr Seemal Jelani Chem-240 28

29. Methyl group Halogens  Electron- releasing substituent  Decreases acidity  Electron- withdrawing substituent  Increases acidity Spring, 2011 Dr Seemal Jelani Chem-240 29

30.  Strongly EWG like NO 2 have acid- strengthening effect  It is more acid-strengthening when it is ortho or para to –OH group  Additional nitro groups further increase the acid strength Spring, 2011 Dr Seemal Jelani Chem-240 30

31.  Thus the acidity of dinitrophenols is comparable to that of carboxylic acids  The cumulative effect of three nitro groups makes 2,4,6- trinitrophenol nearly as strongly acidic as a mineral acid and it is known as picric acid Spring, 2011 Dr Seemal Jelani Chem-240 31

32.  In general phenols are very acidic.  They are caustic towards flesh and very poisonous  Phenol itself is used as disinfectant either in solution or mixed with Ca(OH )2, for toilets, stables, floors and drains  It is also used as a caustic for animals bites Spring, 2011 Dr Seemal Jelani Chem-240 32

33. Spring, 2011 Dr Seemal Jelani Chem-240 33 Reactions of phenols

34.  They give two types of reactions a) The reactions due to the –OH b) The reactions due to the aromatic ring OH-group reactions involve the cleavage of the O-H bond, as e.g. In the formation of salts, ethers and esters, so they resemble alcohols in this respect Spring, 2011 Dr Seemal Jelani Chem-240 34

35.  Most of the reactions of phenols fall in the second category in which phenols distinctly differ from alcohols The striking feature High reactivity of its ring towards ESR, due to the presence of the strongly activating -OH Spring, 2011 Dr Seemal Jelani Chem-240 35

36.  Thus phenols undergoes ESR like nitration, halogenation, Friedel –Crafts reaction and sulfonation characteristics of aromatic compounds  A number of important ESR of phenols involve phenoxide ions which are formed under basic conditions Spring, 2011 Dr Seemal Jelani Chem-240 36

37. This phenoxide is water soluble The –O - of the phenoxide ions is strongly electron releasing and thus more strongly activating than the –OH group Spring, 2011 Dr Seemal Jelani Chem-240 37

38.  Phenoxide ion can therefore react with even weaker electrophiles like carbon dioxide  With phenols special care must be taken to prevent polysubstitution and oxidation Spring, 2011 Dr Seemal Jelani Chem-240 38

39.  Phenols are stronger acid than alcohols therefore they can form salts even with weaker bases  The most phenols can be converted into their salts by aq. NaOH, a much weaker base than the sodium metal which is required to form salts with alcohols, as alcohols do not react with NaOH Spring, 2011 Dr Seemal Jelani Chem-240 39

40.  Most phenols can dissolve in aq. NaOH by forming sodium phenoxides whereas  Most alcohols having more than five carbon atoms do not  This provides a convenient method of distinguishing as well as separating phenols from alcohols Spring, 2011 Dr Seemal Jelani Chem-240 40

41.  Alcohols with five or fewer carbon atoms dissolve in aq. NaOH not by forming sodium salts but because they are soluble in water  2,4,6-ter-butylphenol does not form salt even with sodium metal, why?  Due to steric hindrance to approach of a reagent to the –OH group and to solvation of the phenoxide ion Spring, 2011 Dr Seemal Jelani Chem-240 41

42.  On treatment with alkyl halides in the presence of aq. NaOH, alkyl aryl ethers are formed  With aq. NaOH, a phenol is converted to a phenoxide ions which act as a Nu: and displaces halide ion from the alkyl halide in an SN2 reaction Spring, 2011 Dr Seemal Jelani Chem-240 42

43.  Dialkyl sulphates ca also be used as alkylating agents under these conditions Spring, 2011 Dr Seemal Jelani Chem-240 43

44.  Phenols can be used to form esters  The reaction is carried out with an acid chloride or anhydride in the presence of a base or an acid Spring, 2011 Dr Seemal Jelani Chem-240 44

45.  Acetyl salicylic acid commonly known as Aspirin is prepared by Acetylation of salicylic acid Spring, 2011 Dr Seemal Jelani Chem-240 45

46.  On treatment with conc. Nitric acid, phenol is converted into 2,4,6- trinitrophenol (picric acid)  Mononitrophenols are produced by using dilute nitric acid Spring, 2011 Dr Seemal Jelani Chem-240 46

47.  Reacts readily with an excess of chlorine or bromine in aqueous solution to give 2,4,6-trihalophenols  Phenols have high reactivity therefore no Lewis acid is required  Monohalogenation  Monohalogenation of phenol can be achieved by carrying out the reactions in a solvent of low polarity such as chloroform, carbon tetrachloride or carbon disulfide at Spring, 2011 Dr Seemal Jelani Chem-240 47

48. low temperature  These conditions reduce the electrophilic reactivity of halogens  Monochlorination gives a mixture of o and p-chlorophenols  They differ in BP by 41 0 C and easily can be separated by fractional distillation Spring, 2011 Dr Seemal Jelani Chem-240 48

49.  Monobromination yields p- bromophenol exclusively  o-Bromophenol can be also prepared Spring, 2011 Dr Seemal Jelani Chem-240 49

50.  Friedel Crafts reactions with phenols in the presence of aluminium chloride is complicated by an reaction of the phenol with the Lewis acid  Yield is poor  However alkyl and acyl derivatives of phenols can be prepared by other methods Spring, 2011 Dr Seemal Jelani Chem-240 50

51.  Alkylation of phenols can be achieved by using an olefin as an alkylating agent in the presence of HF Spring, 2011 Dr Seemal Jelani Chem-240 51

52.  Can be obtained by heating alkyl phenyl ethers  Catalyst is aluminium chloride  Reaction is intermolecular process involving substitution of the alkyl group Spring, 2011 Dr Seemal Jelani Chem-240 52

53.  On treatment with conc. H 2 SO 4  25 0 C  Product is ortho  However with increased temperature i.e.100 0 C para product is mainly formed Spring, 2011 Dr Seemal Jelani Chem-240 53

54.  Introduction of Formyl group – CHO into the aromatic ring of phenols  Generally o-positions Spring, 2011 Dr Seemal Jelani Chem-240 54

55.  Reaction with Br-water gives 2,4,6- tri bromophenol  Many phenols when treated with FeCl 3 in dilute aqueous or alcoholic solution, give characteristics colour ranging from violet through blue and green to red  Phenols itself gives violet coloration and cresols give a blue colour Spring, 2011 Dr Seemal Jelani Chem-240 55

56.  The color develops due to the formation of ferric phenoxides ( coordination complexes) which involve an extended delocalization of pi electrons of the aromatic rings through the iron atoms and thus absorb visible light  Phenols show distinct colors with ferric chloride why ? Spring, 2011 Dr Seemal Jelani Chem-240 56

57.  Industrial process from readily available cumene  Forms cumene hydroperoxide with oxygen at high temperature  Converted into phenol and acetone by acid Spring, 2011 Dr Seemal Jelani Chem-240 57

58. Spring, 2011 Dr Seemal Jelani Chem-240 58

59.  From aromatic sulfonic acids by melting with NaOH at high temperature  Limited to the preparation of alkyl-substituted phenols Spring, 2011 Dr Seemal Jelani Chem-240 59