1. Alcohols, Phenols and Thiols By Prof. Dr. Adel M. Awadallah
Organic chemistry for medicine and biology students
Chem 2311
Chapter 7
Alcohols, Phenols and Thiols
By Prof. Dr.
Adel M. Awadallah
Islamic University of Gaza

2. Nomencalture of alcohols
Use the end ol
Examples

4. Hydrogen bonding in alcohols and phenols
Alcohols and phenols form hydrogen bonds, and hence they have relatively high boiling points. This also makes the lower alcohols miscible with water. As the R group becomes larger, the solubility of alcohols in water decreases dramatically.

5. 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.

6. Acidity of Alcohols
Acids are proton donors.

7. The acidity increases as the negative charge at the OH decreases (delocalized):
phenols are more acidic than Alcohols due to resonance effect (delocalization of the negative charge)

8. Nitrophenols are more acidic than phenols due to resonance and inductive effect (The partial neutralization of the negative charge by a nearby positive charge).

9. c) Electron withdrawing groups attached to alcohols increase the acidity of alcohols due to inductive effect.
d) Remember; Thiols are more acidic than alcohols because the sulfur atom is larger than oxygen, and hence carries the negative charge easily.

10. Preparation of ethanol
Ethanol is manufactured by reacting ethene with steam. The catalyst used is solid silicon dioxide coated with phosphoric(V) acid. The reaction is reversible.
Only 5% of the ethene is converted into ethanol at each pass through the reactor. By removing the ethanol from the equilibrium mixture and recycling the ethene, it is possible to achieve an overall 95% conversion.

11. The manufacture of other alcohols from alkenes
Take care of Markovnikov and anti Markovnikov additions

12. Reactions of Alcohols
Acidic dehydration produces alkenes with the more substituted double bond
(OH- is a bad leaving group, but H2O is a good leaving group, so the reaction starts by protonation of the OH group

13. Dehydration of tertiary butyl alcohol

14. Examples

15. Reaction of Alcohols with Hydrogen Halides
The general reaction looks like this:
A tertiary alcohol reacts if it is shaken with concentrated hydrochloric acid at room temperature.

16. The order of reactivity is: I > Br > Cl
Primary Halides:
The reaction is very slow with primary chlorides, and may occur by heating them with ZnCl2 for several hours.
The order of reactivity is: I > Br > Cl
Reaction with phosphorus(III) chloride, PCl3
Alcohols react with liquid phosphorus(III) chloride (also called phosphorus trichloride) to make chloroalkanes.

17. Reacting alcohols with sulphur dichloride oxide (thionyl chloride)
The reaction
Sulphur dichloride oxide (thionyl chloride) has the formula SOCl2.
The two other products of the reaction (sulphur dioxide and HCl) are both gases. That means that they separate themselves from the reaction mixture.
Hydrogen halides, phosphorous halides or thionyl halides cannot replace the hydroxyl group of phenols by halogens

18. Oxidation of Alcohols
Primary alcohols are oxidized to aldehydes using pyridinium chlorochromate (PCC).
Oxidation by KMnO4, K2Cr2O7 or CrO3 dissolved in sulfuric acid
(Jones’ reagent) gives the corresponding carboxylic acids).

19. Oxidation of secondary alcohols (gives ketones)
Oxidation of tertiary alcohols (don’t occur)

20. Polyhydroxy compounds

21. Oxidation of Phenols

22. Antioxidant Phenols
Phenols function as antioxidants. They destroy peroxy free radicals (ROO.)

23. Thiols
Nomenclature
Preparation
R – X + SH- == R – SH X-

24. Reaction of thiols with NaOH
RSH + NaOH = RS- Na H2O
Dislfides