Alcohols, Phenols &Thiols

ALCOHOLS

Classification and Nomenclature of Alcohols Alcohols, and Phenols  Alcohols and phenols may be viewed as organic derivatives of water.  Alcohols and phenols have a common functional group, the hydroxyl group, —OH.  In alcohols the hydroxyl group is attached to an alkyl group, —R.  In phenols the hydroxyl function is attached to an aromatic ring, Ar. Classification and Nomenclature of Alcohols  Alcohols are classified into:

IUPAC Name 1. Select the longest continuous carbon chain that contains OH group. Replace the ending the suffix -ol . 2. If a molecule contains both an -OH group and a C=C or C≡C triple bond. The name should include both the hydroxyl and the unsaturated groups. The -OH group takes preference before the double or triple bonds in getting the lower number. If a compound contains both OH and a double or triple bond, choose the chain that include them both even if this is not the longest chain. -

4- Cyclic alcohol, no. starts from C near to OH 3. In the IUPAC system. The suffix diol is added to the name of the parent hydrocarbon when there are two OH groups. triol is added when there are three OH group Two OH groups on adjacent carbons are known as 1,2-glycols. 2 OH groups on the same carbon make the compound less stable 4- Cyclic alcohol, no. starts from C near to OH

Secondary and tertiary alcohol Common name listing the alkyl substitutents attached to the hydroxyl group, followed by the word alcohol. Primary alcohol CH3OH CH3CH2OH CH2=CHCH2OH Common Methyl alcohol Ethyl alcohol Allyl alcohol IUPAC Methanol Ethanol 2-Propen-1-ol Secondary and tertiary alcohol

Chair form

Physical Properties of Alcohols Solubility As the number of carbons in the alcohol increases, the solubility in water decreases. when No. of OH  Soluble. in H2Oinc. Triols Diols and are more soluble in water than monohydroxy alcohols. Boiling points The boiling points increase with increase in molecular weights. The Increase of alcohol BP. is due to the presence of hydrogen bonding BP. In straight chains is higher than branched

Alcohols are week acids. In isomer BP. Dec. with  in alkyl gp. 3 < 2<1 alcohol BP. Higher than it is alkanes ( hydrogen bond) Alcohols are week acids. Alcohol weaker acids than phenol and carboxylic acids

Acidity of alcohol ROH weaker as acid than H2O ALKOXIDE Hydroxide RO-˃ OH- BASICITY CH3OH IS THE MOST ACIDIC ALCOHOL, BECAUSE ITS COJUGATE BASE IS THE MOST STABLE δ

Synthesis (Preparation) of Alcohols 1. From alkene

2– From alkyl halid

Reducing agents In alkenes, aldehydes, and ketones will broke the = bond (C=C, C=O) and add 2H, but in carboxylic acid will also remove one (O) Ni or Pd or Pt / H2 (very strong will also break the C=C) NaBH4 (weak, FOR ONLY ALDEHYDE & KETONE) LiAlH4 (strong FOR All C=O)

3] From reduction of aldehyd , ketones & carboxylic acid: Reducing agent : NaBH4 /H2O ( for ONLY aldehyde or ketone) H2 / Pt or Pd or Ni, (all=) Li Al H4 /dry ether (all C=O) for (1 , 2 only) 1 1 ROH aldehyde 2 2 ROH ketone Carboxylic acid 1 ROH 2 2 2 2 1 2 2

4] From Grignard reagent: for (1 , 2 & 3) a) with aldehyde : ALDEHYDE GIVE 1&2 ROH KETONE GIVE 3 ROH ESTER GIVE 3 ROH EPOXIDE GIVE 1&2 b) with ketones:

c) with ester: need 2eq. RMgX d) with epoxide:

Reactions of Alcohols 1-Dehydration (Elimination Reactions) : E1 & E2 (Dissociation of R-OH Bond) 1-Dehydration (Elimination Reactions) : E1 & E2 Zaitsev’s Rule If there are different protons can be eliminated with the hydroxyl group or with halogen atom, in this case more than one alkene can be formed, the major product will be the alkene with the most alkyl substituents attached to the double bonded carbon. And the second will be the minor product. symmetrical 2◦ 2◦ or Only one product

2] Reaction with alkyl halides (Substitution Reaction) :

3] Formation of ether

(Dissociation of RO-H Bond) 1- Salt Formation Active metal: Na, K or Mg

Oxidizing agents In alcohols, aldehyde will form the = bond (C=O) and remove 2H, but to oxidize the aldehyde just add (+O) Cu/ Heat (weak) CrO3/ Pyridine (weak) (STRONG):KMnO4, K2Cr2O7, H2Cr2O7, HNO3 1 ROH RCOH RCOOH 2 ROH RCOR’ 2 RCOOH 3 ROH RCOR’ 2 RCOOH Lower carbon number than the used alcohol Basicity solution Acid solution NR Oxidation of alcohol

2] Oxidation: 1 2 3

3] Esterification: alcohol + acid or their derivatives Ester a) Inorganic ester Alcohols reacts with HO-X inorganic acids, X could be: NO NO2 SO3H H2PO3 Cl, Br, F, I

b) Sulphuric acid ester c) Carboxylic acid ester

PHENOLS

Nomenclature and acidity of Phenols Phenols are generally named as derivatives of the simplest member of the family, phenol. Phenols is an hydroxyl group attached directly to a benzene ring e

(NO2) is e with. (deact.gp) acidity (CH3)is dona.gp. acidity Acidity of Phenols Introduction of electron-withdrawing groups, such as NO2 or CN, on the ring increases the acidity of phenols. (NO2) is e with. (deact.gp) acidity (CH3)is dona.gp. acidity Introduction of electron-withdrawing groups, such as NO2 or CN, on the ring increases the acidity of phenols. Alcohols and phenols have weak acidic properties. Phenols are much stronger acids than alcohols.

Preparation of phenols 1-From Diazonium salts: 2-From alkali fusion of sodium benzene-sulfonates:

Salt formation via strong base or active metal Williamson ether synthesis Ester formation Friedel-Crafts acylation: Fries rearrangement Halogenation Coupling with diazonium salts Kolbe-Schmitt Carboxylation Reimer-Tiemann reaction Reactions of Phenols

Williamson ether synthesis Salt formation via strong base or active metal Ester formation Friedel-Crafts acylation: Fries rearrangement Kolbe-Schmitt Carboxylation Reimer-Tiemann reaction Coupling with diazonium salts

2-Reaction of aromatic nucleus of phenol (Electrophilic Substitution) CCl4 Halogenation

Reimer-Tiemann Reaction Mechanism 2 - -2 OH

THIOLS

Thiols and Sulfides Thiols (RSH), are sulfur analogs of alcohols Named with the suffix -thiol SH group is called “mercapto group” (“capturer of mercury”)

Thiols: Formation and Reaction From alkyl halides by displacement with a sulfur nucleophile such as –SH The alkylthiol product can undergo further reaction with the alkyl halide to give a symmetrical sulfide, giving a poorer yield of the thiol

Sulfides Sulfides (RSR), are sulfur analogs of ethers Named by rules used for ethers, with sulfide in place of ether for simple compounds and alkylthio in place of alkoxy

Using Thiourea to Form Alkylthiols Thiols can undergo further reaction with the alkyl halide to give dialkyl sulfides For a pure alkylthiol use thiourea (NH2(C=S)NH2) as the nucleophile This gives an intermediate alkylisothiourea salt, which is hydrolyzed cleanly to the alkyl thiourea

Oxidation of Thiols to Disulfides Reaction of an alkyl thiol (RSH) with bromine or iodine gives a disulfide (RSSR) The thiol is oxidized in the process and the halogen is reduced

Sulfides Thiolates (RS) are formed by the reaction of a thiol with a base Thiolates react with primary or secondary alkyl halide to give sulfides (RSR’) Thiolates are excellent nucleophiles and react with many electrophiles

Sulfides as Nucleophiles Sulfur compounds are more nucleophilic than their oxygen-compound analogs 3p electrons valence electrons (on S) are less tightly held than 2p electrons (on O) Sulfides react with primary alkyl halides (SN2) to give trialkylsulfonium salts (R3S+)

Oxidation of Sulfides Sulfides are easily oxidized with H2O2 to the sulfoxide (R2SO) Oxidation of a sulfoxide with a peroxyacid yields a sulfone (R2SO2) Dimethyl sulfoxide (DMSO) is often used as a polar aprotic solvent