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Chemistry Year 13 > Carboxylic Acids And Derivatives > Flashcards

Carboxylic Acids And Derivatives Flashcards

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1
Q

How are carboxylic acids produced?

A

When primary alcohols or aldehydes are oxidised

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2
Q

Which carboxylic acids are volatile?

A

Carboxylic acids with low relative molecular masses

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3
Q

What is the functional group of carboxylic acids?

A

-COOH

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4
Q

What is a derivative in chemistry?

A

A molecule that is made from a similar compound by a chemical process

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5
Q

Which carboxylic acids are water soluble and why?

A

Carboxylic acids with fewer than six carbon atoms per water molecule. This us because water molecules cab hydrogen bond with the functional group. In aqueous solutions they are only slightly ionised to give low concentrations of hydronium ions and alkanoate ions (carboxylate ions)

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6
Q

Why are carboxylic acids weak acids?

A

Because if their partial ionisation in solution

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7
Q

What reaction is a useful test for the presence of carbon dioxide?

A

The hydrogen ions will react with an aqueous solution of sodium carbonate and produce carbon dioxide

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8
Q

What are some common derivatives of carboxylic acids?

A

Acyl chlorides, acid anydrides, esters and amides

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9
Q

What is the IUPAC nomeclature of carboxylic acids, esters and amides.

A
  • carboxylic acids are named from the parent alkane by replacement of rhe suffix with -oic acid
  • for esters identify the chain that contains the carbonyl group and the one directly attached to the oxygen atom. List the group attached to the oxygen first and introduce the suffix -oate to the parent chain containing the C=O
  • for amides derived from ammonia add the suffix -amide while for those derived from primary amines first list the nitrogen substituent and reinforce the fact that it is bonded to the nitrogen atom by incorporating the prefix N-
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10
Q

How is an ester formed?

A

When an alcohol and a carboxylic acid react together in the presence of a concentrated strong acid catalyst (e.g. sulfuric acid or hydrochloric acid)

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11
Q

What is the general equation for the synthesis of esters from carboxylic acids and alcohols?

A

Check snap camera roll

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12
Q

What have radiocative labelling studies shown in regard to esterifcarion?

A

That in mkst cases the C-O bond in the acid breaks rather than in the alcohol

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13
Q

The reaction to form aan ester from an acid and alcohol is often reffered to as esterfication. What reaction is it an example of and why?

A

It is an example of a condensation reaction since a small molecule (H2O) is eliminated from two carbon-based molecules that form a larger molecule

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14
Q

Ester formation reactions are reversible and produce relatively low yields of esters. How can the equilibrium be shifted towards the product?

A

If water is distilled from the reaction mixture as it forms or if a large excess of alcohol is used

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15
Q

What are esters used for?

A

They are important chemicals in the fragrances and flavourings industry. They have a fruity, sweet smell. They are responsible for many flower scents and fruit flavours. The artificial fruit flavours used in some confectionary products are mixtures of synthetic esters

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16
Q

How can we use the sweet or fruity smell of an ester as a test for the presence of an alcohol or carboxylic acid?

A

If we suspect the compound being investigated is an alcohol, it can be warmed with carboxylic acid such as ethanoic acid in the presence of concentrated sulfuric acid (a catalsyt). Excess acid with its pungent smell can be removed by adding warm aqeous sodium carbonate solution. If the remaining mixture has the sweet smell of an ester this confirms the presence of an alcohol

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17
Q

Esters are used as plasticisers. What are these?

A

Additives mixed into polymers to increase the flexibility of the polymer

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18
Q

Poly(chloroethene) PVC is a strong rigid polymer suitable for making drainpipes. However when treated with up to 18% by mass of an appropriate plasticising ester it can be made into clingfilm. How does this take place?

A

PVC consists of very long polymer chains. The carbon-chlorine bond is strongly polar and there is considerable intermolecular attraction between the polymer chains. Plasticer molecules penetrate between the polymer chains and increase the distance between the chains. The polar effects of the carbon-chlorine bond are weakened and the rigidity of the 3D structure is reduced. As a result the plastic is soft and pliable

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19
Q

Apart from as fragrances and plasticisers what else are esters used for?

A

They are used as solvents for organic compounds. E.g. ethyl ethanoate is a solvent in glues, fragrances and nail varnishes

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20
Q

How are naturally occuring fats formed?

A

Via an esterification reaction in which 1 mole of glycerol reacts with 3 moles of fatty acid in the presence of an acid catalyst and 3 moles of water are eliminated. This forms a triglyceride

21
Q

What is the reverse of an esterification reaction called and how does it take place?

A

Hydrolysis. The ester is hydrolysed by the action of water to reform the acid and alcohol. It requires heating and a strong acid or alkali such as sulfuric acid or sodium hydroxide catalyst. The Acid-catalysed hydrolysis reaction is usually carried out with an excess of water to drive the equilibrium to the desired carboxylic acid

22
Q

What happens in alkaline hydrolysis?

A

An excess or sodium hydroxide is used. The carboxylic acid that forms reacts with excess alkali to form a carboxylate salt. This reaction continually removes carboxylic acid from the equilibrium mixture. The alkaline solution containing the carboxylate salt is neutralised with HCl to give a high yield of the carboxylic acid

23
Q

What are soaps?

A

Carboxylate salts of long chain carboxlyic acids (fatty acids)

24
Q

How are soaps made and what is the process of manufacturing soaps called?

A

Soaps are made my hydrolysing naturally occuring fat and oil triglycerides. The process is called saponification

25
Q

How does the process of saponification take place?

A

Soap is manufactured by boiling fats and oils in aqueous sodium hydroxide. After the boiling is complete, sodium chloride is added to precipitate the soap. Since the hydrolysis is done under alkaline conditions, the product is a mixture of glycerol and the salts of the fatty acids (soaps).

26
Q

Soaps are anionic detergents. What does this mean?

A

The polar negatively charged carbonyl group of a soap is attracted to water. It is hydrophillic. The long, non-polar hydrocarbon chains are attracted to oil rather than water. They are hydrophobic

27
Q

How does a soap break up oil intro droplets by emulsification?

A
  • Dirt, oil and grease mainly consist of non-polar organic molecules that do not dissolve in water. Therefore oil forms a thin film on the waters surface.
  • when soap or detergent molecules are added they accumulate at the oil/water interfave, with the polar ‘head’ of the soap interacting with the water layer and the non-polar hydrocarbon chain interacting with the non-polar organic oil.
  • when the mixture is stirred or shaken the oil breaks up into tiny droplets (emulsification) and is dispersed throughout the water.
  • the droplets are stable because the outside is made up of polar carboxyl groups interacting favourably with water, and the inside is made up of the hydrocarbon segments of the soap interacting with grease
28
Q

How can sodium salta be converted to free fatty acids?

A

By addding a strong acid such as hydrochloric acid. This addition of hydrogen ions moves the equilibrium to the right, producing the insoluble fatty acid

29
Q

What is biodiesel made from?

A

Renewable vegetable oils

30
Q

How is biodiesel made?

A

By transesterification. It is made from rapeseed oil. The triglyceride is converted into the less viscous methyl ester (rape methyl ester) using a sodium hydroxide catalyst and methanol. The transesterification is reversible so an excess of methanol is used to drive the equilibrium to the right. Under optimum conditions this process can produce a 98% yield

31
Q

How would you prepare a pure organic liquid?

A
  • use an appropriate sized flask and ensure that the reaction mixture occupies less than 1/3 of the flasks volume
  • make sure that the condensor is attached to the water supply with the water entering the condensor at the botto. And exiting at the top
  • the flask can then be heated using a water bath. Always add anti-bumping granules to the flask to ensure the smooth boiling of the contents
  • make sure all joints in the apparatus are secure so that volatile chemicals do not escape during the reaction.
  • once the reaction has finished wait for the apparatus to cool before removing it
  • impure products can be partially purified at this stage by reconfiguring the apparatus for distillation and collecting appropriate fractions, or further purification may involve seperation of components using a seperating funnel
32
Q

How do you seperate two immiscible liquids?

A
  • Use a seperating funnel. Make sure that the tap is freely moveable but does not leak and have a clean beaker positioned under the flask at all times.
  • ensure that the tao of the separating funnel is closed and carefully pour the two liquids to be seperated into the funnel.
  • If it is necessary to mix the two liquids place the stopper into the top of the seperating funnel and then, making sure the tap is closed, hold the stopper onto the funnel and invert the whole funnel a number of times. Open the tap to allow any build up of gases to escape.
  • clamp the seperating funnel to stand and wait for the layers to seperate. Make sure you can identify which is the aqueous layer and with is the organic layer
  • to seperate the denser layer from the top layer open the tap carefully and allow the bottom layer to drain into a clean beaker. When the bottom layer is nearly drained slow down the rate of drainage by partially closing the tap
  • then drain the top layer into a beaker
33
Q

How can you tell which is the aqeous layer and which is the organic layer of two liquids?

A

Add a few cm3 of water and the layer that increases in size is the aqueous layer

34
Q

How are acyl groups built into many molecules?

A

By using acyl chlorides and acid anhydrides

35
Q

How are acyl chlorides derived from carboxylic acids?

A

By substitution of the -OH group by a chlorine atom

36
Q

How are acid anydrides derived from carboxylic acids?

A

By substitution of the -OH group by an alkanoate

37
Q

How are acid chlorides and symmetrical anhydrides named?

A

Acid chlorides are named by identifying the parent hydrocarbon chain and adding the suffix -ocyl chloride while symmetrical anydrides utilise the suffix -oic anhydride

38
Q

What are reactions in which acyl groups are introduced into molecules called?

A

Acylations

39
Q

What uses do acylation reactions have?

A

Uses in the pharmaceutical and textile industries. Acylation reactions are used to make drugs such as aspirin and textiles such as cellulose acetate.

40
Q

What do reactions of acyl chlorides with water or an alcohol produce and is the reaction exothermic or endothermic?

A

Reaction of acyl chlorides with water or alcohols is normally a fast exothermic process producing carboxylic acids or esters along with rapid generation of plumes of highly corrosive hydrogen chloride gas

41
Q

What do reactions of acyl chlorides with water or an alcohol produce and is the reaction exothermic or endothermic?

A

Reaction of acyl chlorides with water or alcohols is normally a fast exothermic process producing carboxylic acids or esters along with rapid generation of plumes of highly corrosive hydrogen chloride gas

42
Q

Why do acid anydrides generally make better acylating agents than acyl chlorides?

A

The anhydrides are cheaper to produce and, as they are less reactive, their reactions can be more easily controlled. For acyl chlorides the by-product is hydrogen chlorise but for acid anyhydrides the by-product is the less corrosive carboxylic acidified

43
Q

What do the reactions of acylating agents with ammonia and primary amines produce?

A

Amides and N-substituted amides

44
Q

What mechanism are all acylation reactions examples of?

A

A nucelophillic addition-elimination mechanism

45
Q

What do all nucleophiles in the nucelophillic addition-elimination mechainsm all have?

A

Lone pairs associated with either an oxygen or nitrogen atom and contain a hydrogen atom directly bonded to that oxygen or nitrogen atom.

46
Q

Why do both acyl chlorides and acid anydrides react readily with nucleophiles in the nucleophillic addition-elimination mechanism?

A

Because the electronegative oxygen atoms (im anhydrides) and/or chlorine atoms (in acyl chlorides) polarise the bonds towards the carbon atom of the acyl group. Carbon is the positive end of the polar bond and is exposed to attack by the nucleophiles

47
Q

What is the general nucleophillic addition-elimination mechanism with water?

A

Check snap camera roll

48
Q

What are the four stages the addition-elimination reaction occurs in?

A

1) attraction: the d+ carbon atom of the polar C=O ond attracts the lone pair of a nucleophile
2) Addition: the lone pair of the nucleophile molecule forms a new bond to the carbon atom and the C=O bond breaks producing a saturated ion that has both positive and negative charges
3) elimination: the C-Cl of the acyl chloride or the C-O of the anhydride breaks with the electron pair liberating a chloride ion or ethanoate ion as simultaneously the C=O bond re-forms
4) the new compound is formed by removal of an H+. With ammonia or amine nucleophiles two moles of ammonia or amine are required: one acts as the nucelophile while the other reacts with the acid produced in an acid-base reaction

49
Q

What does it mean if a nucleophile is said to be acylated?

A

An acyl group has replaved a hydrogen atom in the nucleophile

Chemistry Year 13 (16 decks)

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