1. Alcohols, Ethers and Thiols

2. Alcohols (R-OH)
Alcohols are organic compounds that contain the –OH (hydroxyl) functional group attached to the hydrocarbon skeleton (alkyl or aryl)
Simplest alcohol is methanol (CH3OH)
Chemistry, Raymond Chang, 10th edition, McGraw-Hill

3. Alcohols – Hydroxyl Functional Group
Many important biological molecules have one or more hydroxyl groups (sugars, fats, proteins)
Hydroxyl group is involved in many reactions in biological systems such as oxidation, reduction, dehydration
glucose
Biological production of ethanol – fermentation of sugar
serine

4. Naming Alcohols IUPAC nomenclature rules for alcohols:
1) Find the parent compound name, which is the longest continuous carbon chain containing the hydroxyl group
2) Replace “-e” with “-ol”
For example; ethane
ethan(e) + ol
3) Number the parent chain so that the carbon attached to the hydroxyl has the lowest possible number
4) Add substituent names as prefixes to the main name
5) Alcohols with two hydroxyls are named “-diols”
Common names are used for some alcohols, with the name of the alkyl group: isopropyl alcohol, ethylene glycol, ethyl alcohol)

5. Physical Properties of Alcohols
Polar molecules (presence of highly electronegative oxygen atom)
Form hydrogen bonds between themselves and with water molecules
They have high melting and boiling points especially due to hydrogen binding
CH3CH2CH2CH3 (butane) MW = 58, b.p. = -0.5 °C
CH3CH2CH2OH (1-propanol) MW = 60, b.p. = 97.2 °C
Small alcohols (1-4 carbons) are very soluble in water
As the hydrocarbon part (nonpolar) becomes larger relative to hydroxyl (polar) part, alcohols become less soluble (alcohols with 7 or more carbons are almost insoluble)

6. Medically Important Alcohols
Methanol (CH3OH): Used mainly as a solvent, also called wood alcohol, toxic, can cause blindness and even death if ingested
Ethanol (C2H5OH): Used as solvent, beverage and raw material for synthesis of more complex organic compounds, produced by fermentation of sugar
2-Propanol (isopropyl alcohol): used as disinfectant (before and after injection/blood test), as an astringent (skin-drying agent), as industrial solvent / toxic when ingested
1,2,3-Propanetriol (glycerol): viscous liquid, very soluble in water, used in cosmetics and pharmaceutical industry

7. Classification of Alcohols
Alcohols are classified as primary (1°), secondary (2°) and tertiary (3°)

8. Reactions of Alcohols 1) Preparation of alcohols:
2) Dehydration of alcohols:
3) Oxidation reactions:

9. Reactions of Alcohols 1) Preparation of alcohols:
Hydration reaction: addition of water to alkenes (carbon-carbon double bond) – follows Markovnikov rule:
Hydrogenation (reduction) of aldehydes and ketones (by metal catalyst)

10. Reactions of Alcohols
2) Dehydration of alcohols (Elimination of Water):
Alcohols undergo loss of water (dehydration) when they are heated with acid
Reverse process of hydration reaction
Predicting products of alcohol dehydration - Zaitsev’s rule- more substituted alkene is preferred
R-CH2-CH2-OH + H2SO4 ---> R-CH=CH2

11. Reactions of Alcohols 3) Oxidation Reactions:
An oxidation reaction involves gain of oxygen or loss of hydrogen
Alcohols can be oxidized to aldehydes, ketones and carboxylic acids
Most common oxidizing agents are potassium permanganate (KMnO4) and chromic acid (H2CrO4)
Tertiary alcohols can’t be oxidized

12. Ethers (R-O-R)
Ethers are organic compounds that contain the –OR (alkoxy) functional group attached to the hydrocarbon skeleton
-OH group in alcohols is replaced by –OR (alkyl or aryl group instead of hydrogen)
In other words, ethers are compounds in which two alkyl (or aryl) groups are linked by a bridging oxygen

13. Naming Ethers
In IUPAC system, -OR substituent is named as alkoxy group (similar to hydroxy)
CH3-O- (methoxy), CH3CH2-O- (ethoxy)
Ethers are named by placing the two alkyl group names in front of the word “ether”
The two names are placed either alphabetically or by size (smaller first)
examples: dimethyl ether, ethyl methyl ether, ethyl propyl ether

14. Physical Properties of Ethers
1) Ethers are relatively polar molecules (but not as polar as alcohols) 2) Unlike alcohols, they can’t make hydrogen bonds with itself – so lower mp and bp compared to alcohols 3) They can make hydrogen bonds with water – more soluble than alkanes but less than alcohols

15. Chemical Properties and Preparation
Ethers are moderately inert (not very reactive)
Extremely volatile and flammable (easily oxidized in the air), requires great care
Prepared by a dehydration reaction from two alcohol molecules in the presence of acid and heat:
R-OH + R-OH  R-O-R + H2O (heat/acid)
(heated with sulfuric acid at 140 °C)

16. Medical Importance of Ethers
Diethyl ether was the first general anesthetic used (in 1800s) – used in surgeries
How does it work?
Diethyl ether accumulate in the lipid material of the nerve cells in the central nervous system and interfere with nerve impulse transmission
This leads to analgesia, lessened perception of pain and unconsciousness
“William Morton, a Boston dentist,
introduced diethyl ether into surgical
practice in This painting shows
an operation in Boston in 1846 in
which diethyl ether was used as an
anesthetic.
Inhalation of ether vapor produces
unconsciousness by depressing the
activity of the central nervous system”

17. Thiols
Thiols contain sulfhydryl group (-SH), similar to alcohols, but sulfur instead of oxygen
IUPAC rules for naming thiols: similar to alcohols, except “-thiol” is added at the end of the name of the parent alkane
Thiol compounds have strong smells (onion, garlic etc.)

18. Importance of Thiols in Biology
The amino acid “cysteine” is a thiol
Cysteine plays an important role in the structure of proteins (disulfide bonds)
Coenyzme A (acetyl group carrier in many biochemical reactions) is also a thiol
cysteine
Coenzyme A