Principles of organic synthesis

Question 1

synthesis (or syntheses in plural) means

Answer 1

to make something new from what already exists

Question 2

the formula for ethyl propanoate is

Answer 2

CH3-COO-C2H5

Question 3

the two step process for converting bromoethane into ethyl propanoate is

Answer 3

bromoethane → X → ethyl propanoate
X has to be ethanol, so
1) bromoethane → ethanol
heat under reflux and aqueous potassium hydroxide (hydrolysis)
2) ethanol → ethyl propanoate
heat with propanoic acid using an acid catalyst (esterification)

Question 4

the general equation for Grignard reagents is:

Answer 4

R - Mg - X

where X is a halogen, usually Br
where R is an alkyl group, for example an ethyl group

Question 5

grignard reagents are made by

Answer 5

• heating a halogenoalkane under reflux with magnesium in a solvent of dry ether
• dry ether is used because grignard reagents react with water, so dry conditions are needed

Question 6

the equation for the formation of a grignard reagent is:

Answer 6

R-Br + Mg → R-Br-Mg

Question 7

the three steps for the extension of the carbon chain using Grignard reagents are:

Answer 7

1) formation of Grignard Reagent:
R-Br + Mg → R-Br-Mg
2) reaction with either CO2 or carbonyl compound:
i) R-Br-Mg + CO2 → R-COO-Mg-Br
ii) R-Br-Mg + RCHO → R’-CH2O-Mg-Br
iii) R-Br-Mg + RCOR → (R)3C-O-Mg-Br
3) reaction with dilute acid (HCl) to form organic product (an alcohol) :
i) R-COO-Mg-Br + H2O → R-COOH + Mg(OH)Br
ii) R’-CH2O-Mg-Br + H2O → R’-CH2OH + Mg(OH)Br
iii) (R)3C-O-Mg-Br + H2O→ (R)3COH + Mg(OH)Br

Question 8

write the equations for the formation of propan-1-ol:

Answer 8

1) CH3CH2Br + Mg (dry ether) → CH3CH2MgBr
2) CH3CH2MgBr + HCHO → CH3CH2CH2OMgBr
3) CH3CH2CH2OMgBr + H2O (H+ from dilute acid)→ CH3CH2CH2OH + Mg(OH)Br