Chapter 26 - Carbonyls and carboxylic acids

Question 1

whats made when an aldehyde is oxidised and what are the reagents and conditions

Answer 1

aldehydes can be oxidised to carboxylic acids when refluxed with acidified dichromate ions usually Kr2Cr2O7 (shown as [O]) and dilute H2SO4

Question 2

how do you distinguish between aldehydes and carboxylic acids

Answer 2

test for a carbonyl using 2,4-DNP and if a carbonyls present an orange/yellow precipitate will form

then use tollens reagent if an aldehyde is present then a silver mirror is formed as Ag ions are reduced if nothing happens its a ketone

Question 3

how do you test for a carbonyl functional group

Answer 3

test for a carbonyl using 2,4-DNP and if a carbonyls present an orange/yellow precipitate will form

Question 4

what does tollens reagent do to an aldehyde

Answer 4

it reduces it to a carboxylic acid

Question 5

what is tollens reagent made up of

Answer 5

silver nitrate in aqueous ammonia

Question 6

whats bradys solution and whys it used

Answer 6

its 2,4-DNP dissolved in methanol and sulfuric acid
its often used in practicals as its less hazardous the 2,4-DNP alone which can easily explode

Question 7

whats formed in the reaction between an acyl chloride and ammonia

Answer 7

a primary -amide and ammonium chloride

Question 8

whats formed in the reaction between an acyl chloride and a primary amine

Answer 8

a secondary -amide and an -ammonium chloride

Question 9

what compounds undergo nucleophilic addition-elimination reactions

Answer 9

acyl chlorides

Question 10

what type of covalent bonds from between a nucleophile and a c-atom

Answer 10

a dative covalent bond

Question 11

how do acyl chlorides from amines

Answer 11

they react with ammonia/amines which acid as nucleophiles and donate a lone pair of electrons on the nitrogen

Question 12

how do acid anhydrides react

Answer 12

they react similarly to acyl chlorides but are less reactive and can be used when acyl chlorides are too reactive and instead of HCl being produced its a carboxylic acid

Question 13

what does ethanoyl chloride (an acyl chloride) react vigorously with to produce

Answer 13

ethanoic acid and HCl
(violent reaction and HCl is dense)

Question 14

what does ethanoyl chloride react with phenol to form

Answer 14

phenyl ethanoate + HCl

Question 15

what does ethanoyl chloride reacting with propan-1-ol form

Answer 15

propyl ethanoate and HCL

Question 16

how do acyl chlorides react with alcohols to form esters

Answer 16

acyl chloride + alcohol/phenol = ester + HCl
HCl is a gas at room temp and its a vigorous reaction (not as vigorous with phenols)

Question 17

why type of reaction is the reaction between NaBH4 and propanone

Answer 17

nucleophilic addition

Question 18

what type of fission breaks the pi-bond in the c=o bond (in reduction by NaBH4)

Answer 18

heterolytic fission

Question 19

what do you get when you reduce a ketone with NaBH4 (2[H] as a reducing agent)

Answer 19

a secondary alcohol

Question 20

what do you get when you reduce an aldehyde with NaBH4 (2[H] as a reducing agent)

Answer 20

a primary alcohol

Question 21

what does NaBH4 do to carbonyls and under what conditions

Answer 21

reduces them when warmed with them in an aqueous solution

Question 22

do ketones undergo oxidation reactions and why/why not

Answer 22

they DONT as their not reactive enough

Question 23

what type of reactions do carbonyls undergo

Answer 23

nucleophilic addition

Question 24

whats the c=o bond like in carbonyls

Answer 24

the double bonds made up of a sigma bond and a pi bond. the c=o bond is polar as the oxygen is more electronegative than the carbon so the electron density in the double bond is closer the the oxygen.
therefore carbonyls react with some nucleophiles as its attracted to the delta positive carbon atom a adds across the double bond

Question 25

whys the reaction of carbonyl compounds with HCN useful

Answer 25

it provides a means of increasing the length of the carbon chain

Question 26

whats used to provide HCN/hydrogencyanide in reactions

Answer 26

sodium cyanide and sulfuric acid

Question 27

what forms when HCN reacts with an aldehyde

Answer 27

a hydroxynitrile

Question 28

whats the solubility of carboxylic acids like

Answer 28

the c=o and o-h bonds in carboxylic acids are polar, allowing carboxylic acids the form H bonds with water molecules carboxylic acids with up to 4 carbons are soluble in water as the number of c atoms increases the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecules

Question 29

what redox and neutralisation reactions do carboxylic acids take place in and what happens to the carboxylic acid

Answer 29

redox reactions with metals neutralisation reactions waith bases (alkalis, metal oxides and carbonates) the carboxylic acid forms a carboxylate c=o and c-o minus

Question 30

whats the strength of carboxylic acids like

Answer 30

they are weak acids so they only partially dissociate in water eg methanoic acids makes H+ and HCOO-

Question 31

how do carboxylic acids react with metals

Answer 31

in a redox reaction to form hydrogen and a carboxylate salt

Question 32

how do carboxylic acids react with metal oxides

Answer 32

they react to form salt and water

Question 33

how do carboxylic acids react with alkalis

Answer 33

they react to form salt and water this is an aqueous neutralisation reaction

Question 34

how do carboxylic acids react with carbonates

Answer 34

they react to form salt, water and carbon dioxide if the acids in excess the solid carbonate would disappear they are only a few organic compounds acidic enough to react with carbonates

Question 35

what are the derivatives of carboxylic acids (4)

Answer 35

esters acyl chlorides acid anhydrides amide

Question 36

how are acid anhydrides formed

Answer 36

by the removal of a water molecule from two carboxylic acid molecules

Question 37

how do you test for the carboxyl group using reactions

Answer 37

the neutralisation reaction of carboxylic acids with carbonates gives CO2 off as carboxylic acids are the only common organic compound acidic enough to react with carbonates

Question 38

how to name an ester

Answer 38

the alcohol becomes an -yl at the start eg. ethyl while the carboxylic acid becomes an -oate eg propanoate

Question 39

how can an ester be made from a carboxylic acid and an alcohol

Answer 39

when a carboxylic acid and alcohol are warmed with a small amount of concentrated H2SO4 and ester and H2O are formed

Question 40

whats reversible acid hydrolysis alkaline hydrolysis

Answer 40

acid hydrolysis = reversible alkaline hydrolysis = irreversible

Question 41

how can esters be hydrolysed with acid (acid hydrolysis) and what products are formed

Answer 41

this is the opposite of esterification an ester is heated under reflux with aqueous dilute acid the ester is broken down by water with the acid being the catalyst the products are a carboxylic acid and an alcohol

Question 42

how can esters be hydrolysed with an alkali and whats this known as

Answer 42

this is saponification and its irreversible an esters heated under reflux with aqueous hydroxide ions this produces a salt and an alcohol an alcohol and a carboxylate ions are formed

Question 43

how can acyl chlorides be prepared

Answer 43

the parent carboxylic acid reacts with thionyl chloride (SOCl2) the products are SO2 and HCl as gases and the acyl chloride this reaction should be carried out in a fume cupboard.