What's in a Medicine

Question 1

What happens to the solubility of alcohols with increasing length of hydrocarbon chain?

Answer 1

Solubility decreases as chain length increases as influence of -OH group in hydrogen bonds becomes weaker

Question 2

What reagent is used for oxidation of alcohols

Answer 2

Using acidified potassium dichromate ( VI) K2Cr2O7 solution. The orange dichromate ion is reduced to green chromate (III) ions in the reaction

Question 3

What are 1) Primary alcohols, 2) Secondary alcohols, 3) Tertiary alcohols oxidised into?

Answer 3

1) Aldehydes (partial oxidation) then carboxylic acids (full oxidation in reflux)
2) Ketones
3) Tertiary alcohols cannot be oxidised

Question 4

How are alcohols dehydrated?

Answer 4

Alcohols are dehydrated into alkenes using reflux with concentrated sulphuric acid; this is an elimination reaction

Question 5

How does esterification work?

Answer 5

An alcohol and carboxylic acid is reacted under reflux with concentrated HCl or H2SO4. Since the reaction is reversible, the ester must be distilled and purified

Question 6

What is an alternative agent to carboxylic acid to produce a higher yield of ester?

Answer 6

Acid anhydrides are more reactive than carboxylic acids and react completely with alcohols with warming to give a higher yield of ester.

Question 7

Order phenol, carboxylic acid, ethanol, water in terms of acidity

Answer 7

ethanol < water < phenol < carboxylic acid

Question 8

Can phenols and carboxylic acids react with both strong bases (NaOH) and carbonates?

Answer 8

Both can react with strong bases, however phenols and alcohols do not dissociate H+ strong enough to react with carbonates

Question 9

What’s an alternative form of esterification?

Answer 9

Acid anhydride + phenol –> ester + carboxylic acid

Phenols don’t react with carboxylic acids to produce esters

Question 10

What are the two ways of esterifying salicylic acid?

Answer 10

Reacting the phenol -OH group with an acid anhydride, producing aspirin. Or reacting the -COOH group with an alcohol (with methanol to produce oil of wintergreen)

Question 11

What is the functional group for ether?

Answer 11

R-O-R

Question 12

What is the functional group for acid anhydrides?

Answer 12

-COOCO- which is two carbonyl groups joined by an atom

Question 13

What are some properties of esters?

Answer 13

Sweet, fruity smell. Low boiling points, good solvents for polar molecules

Question 14

What are the 12 principles of green chemistry?

Answer 14

Better atom economy
Prevention of waste products
Less hazardous chemical synthesis
Design safer chemical products
Use safer solvents
Lower energy usage
Use renewable feedstocks
Reduce reagents used and the number of steps
Use more selective catalysts
Design chemical products for degradation
Employ real time process monitoring
Use safer chemical processes

Question 15

Describe and explain the steps of recrystallisation

Answer 15

1) Dissolve then filter the crude product with the minimum amount of hot solvent to remove insoluble impurities
2) Leave filtrate to cool until crystals form
3) Wash solid crystals with cold solvent then vacuum filtrate to remove soluble impurities
4) Dry crystals in oven or leaving in open

Question 16

Describe the steps for thin layer chromatography (TLC)

Answer 16

1) Spot the test mixture and reference samples on a pencil line 1cm above the base of the paper/silica plate, pencil used so it won’t run in solvent
2) Suspend the plate in a beaker containing the solvent and cover the beaker with a watch glass to prevent the solvent from evaporating
3) Remove the plate when the solvent front is near the top, mark how far the solvent has reached, allow the plate to dry in a fume cupboard
4) Locate any spots with iodine or a UV lamp
5) Match the heights reached (Rf values) with known substances to determine purity of sample

Question 17

How can purity of a substance be determined by melting point?

Answer 17

By heating a sample of the organic solid in a capillary tube where the change of state can be observed and compared to known values