no longer an exclusively vicarious one.

Wednesday, February 23, 2005

Chemistry: acidic: 5

5. Esterification is a naturally occurring process which can be performed in the laboratory.

Describe the difference between the alkanol and alkanoic acid functional groups in carbon compounds
A functional group is an atom or group of atoms that reacts in a characteristic way in different carbon compounds. The hydroxy functional group, -OH, in alkanols provides their characteristic properties, such as high melting points and boiling points. This is because of the hydrogen bonding between the hydroxy groups
The carboxylic acid functional group, -COOH, in alkanoic acids can lose a hydrogen ion and behave as a weak acid.

Identify the IUPAC nomenclature for describing the esters produced by reactions of straight-chained alkanoic acids from C1 to C8 and straight-chained primary alkanols from C1 to C8

Alkanol
Alkanoic acid
methanoic
ethanoic
propanoic
butanoic
pentanoic
hexanoic
heptanoic
octanoic
methanol
methyl methanoate
methyl ethanoate
methyl propanoate
methyl butanoate
methyl pentanoate
methyl hexanoate
methyl heptanoate
methyl octanoate
ethanol
ethyl methanoate
ethyl ethanoate
ethyl propanoate
ethyl butanoate
ethyl pentanoate
ethyl hexanoate
ethyl heptanoate
ethyl octanoate
propanol
propyl methanoate
propyl ethanoate
propyl propanoate
propyl butanoate
propyl pentanoate
propyl hexanoate
propyl heptanoate
propyl octanoate
butanol
butyl methanoate
butyl ethanoate
butyl propanoate
butyl butanoate
butyl pentanoate
butyl hexanoate
butyl heptanoate
butyl octanoate
pentanol
pentyl methanoate
pentyl ethanoate
pentyl propanoate
pentyl butanoate
pentyl pentanoate
pentyl hexanoate
pentyl heptanoate
pentyl octanoate
hexanol
hexyl methanoate
hexyl ethanoate
hexyl propanoate
hexyl butanoate
hexyl pentanoate
hexyl hexanoate
hexyl heptanoate
hexyl octanoate
heptanol
heptyl methanoate
heptyl ethanoate
heptyl propanoate
heptyl butanoate
heptyl pentanoate
heptyl hexanoate
heptyl heptanoate
heptyl octanoate
octanol
octyl methanoate
octyl ethanoate
octyl propanoate
octyl butanoate
octyl pentanoate
octyl hexanoate
octyl heptanoate
octyl octanoate

Explain the difference in melting point and boiling point caused by straight-chained alkanoic and straight-chained primary alkanol structures
Straight-chained structures do not have any branches on the hydrocarbon chain.A primary alkanol has the -OH group at the end of the hydrocarbon chain.The high melting points and boiling points in alkanols is due to hydrogen bonding between the O in one molecule and the H of an -OH in a nearby molecule.









The ability of the -COOH group to be involved in two hydrogen bonds gives an alkanoic acid an even higher boiling point than that of a similar sized alkanol. Two hydrogen bonds can occur between a pair of alkanoic acid molecules because the electrons in the bond between the H and its attached O in COOH is weak.







Identify esterification as the reaction between and acid and an alkanol and describe, using equations, examples of esterification
An acid, containing the -COOH functional group, can react with an alkanol, containing the -OH functional group, to produce an ester and water. R-OH + HOOC-R! R-OOC-R! + H2Oalkanol acid ester water
If an oxygen-18 isotope, O, is used in the alkanol only, it is found in the ester, but not in the water product. Use of this tracer shows that the O in water comes from the acid. R-OH + HOOC-R! R-OOC-R! + H2Oalkanol acid ester water
The reaction is reversible and comparable quantities of alkanol, acid, ester and water are present at equilibrium.
Common names, rather than systematic names, are often used to obtain the ester name: CH3OH + HOOCCH3 CH3OOCCH3 + H2OCommon: methyl alcohol acetic acid methyl acetate waterSystematic: methanol ethanoic acid methyl ethanoate CH3CH2OH + HOOCH CH3CH2OOCH + H2OCommon: ethyl alcohol formic acid ethyl formate waterSystematic: ethanol methanoic acid ethyl methanoate

Describe the purpose of using acid in esterification for catalysts
Esterification is catalysed by the addition of a small amount of acid. Esterification is called a condensation reaction because a water molecule condenses out.
Only a few drops of concentrated acid needs to be added to a mixture of alkanol and alkanoic acid to catalyse the reaction.
If concentrated sulfuric acid is added in large amounts, say 5% to 10% of the reaction volume, it can have a significant effect on the position of equilibrium. Concentrated sulfuric acid is a dehydrating agent, that is, it has a strong affinity for water. If a significant amount of sulfuric acid is present, it will shift the equilibrium position to the right by absorbing water. This increases the yield of ester (5-10% of the reactant volume). However using large amounts of sulfuric acid is wasteful, uneconomic and complicates the separation of ester from the reaction mixture.

Explain the need for refluxing during esterification
Esterification requires heat for the reaction to reach equilibrium within an hour, rather than after many days. When the reaction mixture is heated, volatile components, such as the reactant alcohol and the product ester, could escape. This problem is overcome by refluxing the reaction mixture.
A condenser is placed on top of the reaction vessel so that any volatile components pass into the condenser. The condenser can be water or air-cooled and causes the volatile components to condense back to liquid and fall back into the reaction mixture, thereby also increasing the yield of ester collected.
Refluxing also improves the safety of the operation, as the volatile components are flammable.

Outline some examples of the occurrence, production and uses of esters
A number of compounds with characteristic fragrances have similar chemical composition and are called esters. Many flowers and fruits produce volatile esters. Many of the essential oils of plants contain them, and animal fats and fish and plant oils are also esters. Foods, sweets and other products like perfumes contain artificial flavourings and fragrances, many of which are esters.
Aspirin: salicylic acid (2-hydroxybenzoic acid) condenses with ethanoic acid to produce the ester acetylsalicylic acid.
Solvent in nail polish remover and paints: Ethyl acetate (ethanoate)
Toothpaste: propyl hydroxybenzoate
Esters are used :
- as artificial perfumes or scents as they emit a sweet smell.
- in making artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc
- as industrial solvents for making cellulose, fats, paints and varnishes
- as solvents in pharmaceutical industries
- as softeners in plastic industries and molding industries
Essences (flavourings):
- methyl butanoate (apple)
- ethyl methanoate (rum essence)
- ethyl butanoate (pineapple)
- pentyl ethanoate (banana)
- octyl butanoate (orange)
- methyl ethanoate and ethyl ethanoate (solvent)
Identify data, plan, select equipment and perform a first-hand investigation to prepare and ester using reflux
Place 12mL of 1-butanol, 9mL of concentrated ethanoic acid (glacial acetic acid) and 1mL of concentrated sulfuric acid in a 50mL pear shaped flask.
Add a few boiling chips followed by condenser as shown in diagram 1.
Heat the mixture under reflux in a hot water bath for about 30 minutes and then allow to cool for 5 minutes.
Reflux:
Separation:

Distillation:










Pour the mixture into a separating funnel containing about 10-15mL water. Shake and allow to separate. The aqueous layer, which contains most of the sulfuric acid, is the lower layer and is discarded.
Pour the top layer into a small beaker. Add a few r.g. of solid Na2CO3(s) until effervescence ceases. Pour back into the separating funnel. Separate the mixture and discard the lower aqueous layer.
Pour the organic layer into a small beaker and add fused CaCl2 to dry the organic layer.
Decant into a 50mL pear-shaped flask. Distil the product as below. The boiling point of the ester is 126.5°C.
An ester was produced from the reaction mixture, of a purple colour. This ester was butyl ethanoate. It was then purified. The separating funnel was used to remove most of the sulfuric acid, which was in the lower, (denser) aqueous layer of the mixture. The remaining ester was then yellow. NaCO3 was added to completely react with the remaining acid, then it was put through the separating funnel again. CaCl2 was added to use up the remaining water, then the ester was distilled. This final product was clear in colour. The boiling point of the ester was 162°C.
1-butanol + ethanoic acid water + butyl ethanoate
CH3CH2CH2CH2OH + CH3COOH H2O + CH3COOCH2CH2CH2CH3
Na2CO3 was added to react with any remaining acid.
Na2CO3(s) + H2SO4(aq) + CH3COOH(aq)
Then CaCl2(s) was added to remove any remaining water.
CaCl2(s) + H2O(l) CaO + 2HCl(aq)
Distilling the ester was the final step and this was done by evaporating the ester (at about 126°C), then condensing the vapour. The condensed vapour fell through the condenser to drip out into the beaker at the other end.

Process information from secondary sources to identify and describe the uses of esters as flavours and perfumes in processed foods and cosmetics
Esters are used :
- as artificial perfumes or scents as they emit a sweet smell.
- in making artificial food flavours that are added in many edible items like ice creams, soft drinks, sweets, etc
- as industrial solvents for making cellulose, fats, paints and varnishes
- as solvents in pharmaceutical industries
- as softeners in plastic industries and molding industries
Essences (flavourings in food):
- methyl butanoate (apple)
- ethyl methanoate (rum essence)
- ethyl butanoate (pineapple)
- pentyl ethanoate (banana)
- octyl butanoate (orange)
- methyl ethanoate and ethyl ethanoate (solvent)
In cosmetics, esters can help improve the feel of a product that they are blended into since their physical and chemical properties, including viscosity, fluidity and melting point, can be altered by varying the combination of fatty acid and alcohol employed. Esters are used in nail products and skincare products, as well as in sunscreen (octyl methoxycinnamate) and lipstick (2-propyl myristate).

sorry no pics

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