Alcohol Ett Hi Och Me Dl

7/24/2019 Alcohol Ett Hi Och Me Dl

1/18

Information,


2/18

Alcohols, ethers, thiols, and phenols.


3/18

Alcohols, ethers and thiols

Alcohols are built with carbohydrate chains and hydroxyl (-OH) group attached to them. Ethanol

belongs to a homologous series called alcohols with general formula nH!n"#OH. All members of

the series shows similar properties. $hey differ only in the length and structure of the

hydrocarbon chain. Alcohols are deri%ed from al&anes by substituting an 'OH group for an ' H

atom.

$hey are named from parent al&ane by omitting the final 'eand adding the ending 'ol.

C C OH

H

H

H

H

H

R OH

ethanol

general formula of alcohols

HOH methanol

HH

!OH ethanol

HH!H!OH propan-#-ol

HH(OH)H!H propan-!-ol

HH!H!H!OH butan-#-ol

or al&ohols containing more than two atoms,

isomeric compounds are possible. $o distinghish

between these, it is necessery to label the position

of the OH group. $he hydrocarbon-chain is alwaysnumbered from the end with gi%es the lowest

number for the position of the functional group.

$hus, HH!H!H!OH is named butan-#-ol, not

butan-*-ol. +ropan-#-ol and propan-!-ol are

isomers.


4/18

lassification of alcohols

Alcohols can be classified by the number of carbon atoms bonded to the -OH group carbon. A

primary (#o) al&coholcontains one carbon bonde to the -OH carbon. A secondary (!o) alcohol

contains two carbon bonded to the -OH carbon. A tertiary (o) alcoholcontains three carbons

bonded to the -OH carbon.

CH3 CH OH

CH3

CH3 CH OH

CH3

CH3

OHCH2CH3

one carbon two carbonsthree carbons

Primary (10) Seconary (2

0) !ertiary (3

0)


5/18

Alcohols (cont.)

ome alcohols, particularly biologically occurring ones (sacharides), contain more than one 'OH

group in their molecule. $hey are &nown as polyhydricalcohols.Examples of their names

ompounds, in which the 'OH group is directly attached to the ben/ene ring are called phenols.

$he presence of the aromatic ring modifies properties of the 'OH group and they react other

way than aliphatic alcohols.

C C OH

H

H

HO

H

H

C C

H

OH

HO

H

H

C

H

H

OH

ethane"1#2"iol $ro$ane"1#2#3"triol

+hysical properties of alcohols. On can thin& of alcohols

as being deri%ed for water by replacing one of the H

atom by an al&yl group. 0i&e water molecules, alcohol

molecules are polar because of the polar 'OH bond. 1n

both water and alcohols, there is a special sort of strongattracti%e force between the moleculesdue to hydrogen

bonds. Hydrogen bonds are not so strong as co%alent

bonds, but are stronger than the other attracti%e forces

between co%alent molecules.

OH

H

OR

H

water alcohol

OHH

OH

H

ORH

O RH

re$resents a hyrogen bon


6/18

Alcohols (cont.)

OR

H O HH

2hen the li3uid boils, these forces must be bro&en so the molecule escape

from the li3uid to form a gas. $his explains why the boiling points of

alcohols are higher than the those of corresponding al&anes with the similarrelati%e molecular mass (4t). or example, ethanol (4t5 *6) is a li3uid, while

the propane (4t5 **) is a gas in 7$. Hydrogen bonding between alcohol and

water molecules explains why the two li3uids mix together.

8ame ormula olubility 9g:#;; g water.;

+entan-#-ol HH! H! H! H!OH !.?

Hexan-#-ol HH! H! H! H! H!OH ;.6

$able shows the solubility of some alcohols in water. As the hydrocarbon-chain becomes longer,

the influence of the 'OH group on the properties of the molecule becomes less important. o the

properties of higher alcohols get more and more li&e those of the corresponding al&ane.


7/18

ubstitution reactions of alcohols

1n strongly acidic solution alcohols undergo substitution readily because a protonated alcohol

contains a %ery wea&ly basic lea%ing group ' water. All alcohols undergo readily with H1 and H=r

to yield al&yl halides.

All alcohols undergo readily with H1 and H=r to yield al&yl halides.

1o, 2oor 3oROH + HI (HBr)

RI (RBr) + H2O

$ertiaty al&ohols , allilic alcohols, and ben/ylic alcohols react readily with Hl primary and

secondary alcohols are less reacti%e and re3uired a catalyst, such as /in& chloride, @nl !.

ummary of the reacti%ity of differrent types of alcohols

HOH #;7OH !o7OH o 7OH allylic and ben/ylic alcohols

1ncreasing reacti%ity toward HB

%ery wea& base# goo lea%ing grou$

' H2OOH

Hr

"

CH3CH2 rCH3CH2H

'

CH3CH2 OH


8/18

Elimination reactions of alcohols

2hen heated with the strong acid, an alcohol with -hydrogen can undergo dehydration(loss of

water) to yield an al&ene.

CH2 CCH3

CH3

OHH

CH2 CCH3

OHH

H

CH2 CH

OHH

H

CH2 C

CH3

CH3' H2O

CH2 CHCH3 ' H2O

CH2 CH2 ' H2O

"hyrogen

ummary of the reacti%ity of primary, secondary and tertiary of alcohols toward dehydration

#;7OH !o7OH o7OH

1ncreasing ease of dehydration


9/18

Esters of alcohols

Cnder the proper reaction conditions alcohols and acids react, losing water, to yield esters.

7eaction of alcohol with carboxylic acid yields carboxylic ester, called simply ester. $hese

compounds will be discuss in in lecture about carboxylic acids. 7eaction of the alcohol with

the inorganic acid or its chloride can yield an inorganic ester of an al&ohol, a compound in

which the HO- of the inorganic acid is replaced by 'O7 of the alcohol.

HO O2 O2RO

POH

O

OH

POH

O

OH

HO RO

nitric aci an al&yl nitrate

$hoshoric aci an al&yl $hos$hate

+hoshate groups are common lea%ing groups in biochemical reactions phosphate esters are

biologically synthetic intermediates and energy storehouses in li%ing organisms.


10/18

Oxidation of al&ohols

Depending of the conditions of reaction, primary alcohols can be oxidised to aldehydes or to

carboxylic acids. econdary alcohols, howe%er, can be oxidi/ed only to &etones. $ertiary

alcohols resist oxidation in al&aline solutions. 1n acidic solutions tertiary alcohols undergo

dehydration to yield al&enes, which then are oxidi/ed.

RCH2OH

*O+

loss of 2 HRCH

O*O+

gain of O RCOH

O

RCHR,

OH*O+

loss of 2 H

RCR,

OH

R,,

*O+

no reaction

RCR,

O

alehye carbo-ylic aci

&etone

10.

20.

30.


11/18

Ethers

Ethers are deri%ed from al&anes by substituting an al&oxy group (-O7) for an 'H atom. or

example.

HH!-O-H!H ethoxyethane

HH!H!-O-H methoxypropane

$he longer hydrocarbon chain is chosen as a parent al&ane.

+hysical properties of ethers. One can thin& of ethers as being deri%ed from water by replacing

boththe H atoms by al&yl groups.

Ether molecules are only slightly polar and the attracti%e forces between molecules are relati%ely

wea&. $here are no H atoms attached to the oxygen to form hydrogen bonds between ether

molecules. $he boiling point of an ether is similar to that of the al&ane with corresponding relati%e

molecular mass. 0i&e al&anes, the lower ethers are %ery %olatile and dangerously flammable.

Ethers are only slightly soluble in water, but mix well with other nonpolar molecules such as

al&anes.

HO

H

RO

R,


12/18

$hiols

$hiol is an organosulfur compoud that contains a sulfur-hydrogen bond (-H).$hiols are the

sulfur analogue of an alcohol. $he H functional group is referred to as either a thiol groupor a

sulfhydryl group.$hiols are often referred to as mercaptans. $hiols and alcohols ha%e similar

molecular structure. $he --Hangles approach ;F. 1n the solid or molten li3uids, thehydrogen-bondingbetween indi%idual thiol groups is wea&, the main cohesi%e force being %an

der 2aals interactions between the highly polari/able di%alent sulfur centers. Due to the small

electronegati%ity difference between sulfur and hydrogen, an -H bond is less polar than the

hydroxyl group. $hiols ha%e a lower dipole moment relati%e to the corresponding alcohol.

8omenclature. $he preferred method (used by the 1C+A) is to add the suffix -thiolto the nameof the al&ane. $he method is nearly identical to naming an alcohol. Example HH would be

methanethiol, etc. An older method, the word mercaptanreplaces alcoholin the name of the

e3ui%alent alcohol compound. Example HH would be methyl mercaptan, Gust as H

OH is

called methyl alcohol.

+hysical properties. 4any thiols ha%e strong odoursresembling that of garlic. $he odours ofthiols are often strong and repulsi%e, particularly for those of low molecular weight. &un& spray

is composed mainly of low molecular weight thiol compounds. 4ost gas odorants utili/ed

currently contain mixtures of mercaptans and sulfides, with t-butyl mercaptanas the main odour

constituent.

$hiols show little association by hydrogen bonding, with both water molecules and among

themsel%es. Hence, they ha%e lower boiling points and are less soluble in water and other polar


13/18

$hiols

ust as H! is more acidic than H!O, thiols are more acidic than alcohols. $he reason for the greater

acidity is that the larger sulphur atom can better disperse the negati%e charge of the anion. $hiols can

be prepared by nucleophillic substitution reaction of al&yl halides and sodium hydrogen sulphide (8-

H) .

CH3CH2 (r ' SH CH3CH2 SH ' (r

One important reaction of the thiols is their con%ersion to disulphides (7-7)when treating with

midl oxidi/ing agent such as O!or H!O!

HH!-H " H-H!H HH!---H!H " H!O

$he thiol groups in proteins can be oxidi/ed to disulphide groups. $he '-- bridge bonds two

protein molecules and hold them in their necessery shapes

SHSH

SH SH S

SS

S

*O+

$he precipitation of en/ymes and other soluble proteins containing 'H groups by hea%y metal

ions such as Hg!"is a principal reason that compounds containing these ions are poisonous.


14/18

+henols

ompounds that ha%e a 'OHgroup directly attached to ben/ene ring are called phenolI. $hus,

phenolis a specific name for hydroxyben/ene and it is the general name for family of

compounds deri%ed from hydroxyben/ene.

ompounds that ha%e a 'OH group attached to polycyclic ben/oid ring are chemically similar to

phenol, but they are calle naphtholsand phenathrols(name deri%ed from name of parent

polycyclic arene).

$he methyl phenols are commomlly called cresols.

OH OHH3C

$henol /"methyl$henol

OH

OH

OH

8

910

1 1 12

22

3

34 45 56

6

77

8

1"na$htol 2"na$htol "$henanthrol

CH3HO HO

CH3

HO

H3C

/"methyl$henol

($"cresol)

3"methyl$henol

(m"cresol)

2"methyl$henol

(o"cresol)


15/18

+henols (cont.)

$he ben/enediols ha%e also tri%ial names

8aturally occuring phenols

OHHO HO

OH

HO

HO

1#/"beneneiol

(hyrouinon)

1#3"beneneiol

(resorcinol)

1#2"beneneiol

(catechol)

OHHO HO

OH

HO

HO

1#/"beneneiol

(hyrouinon)

1#3"beneneiol

(resorcinol)

1#2"beneneiol

(catechol)

HO

OH

HHHO CH3 (CH3)2

OH

H

OH OH O

OH

4

COH2

O

H

estraiol

(fermale se- hormone) tetracyclines (antibiotics)

(4 5 Cl# 5 H6 aureomycin 4 5 H# 5 OH. terramycin))


16/18

7eactions of phenols

Although phenols are stucturally similar to alcohols, they are much stronger acids. Jreater acidity of

phenol relati%e to alcohols using of resonanse theory.

OH

H2O+

O

H3O'

+

moerate resonance

stabiliation

$heno-ie ion

large resonance stabiliation

charge is elocate

7nion is more

stabilie than

the aci


17/18

7eactions of phenols7eactions with strong bases.

+henols react with carboxylic acids anhydrides and acyl chlorides to form esters. $hosereactions are 3uite similar to those of alcohols

OH ' aOH O"a

'

OH ORC

O

2 O+ CR

O

' RCO"

O

OH ' RCCl

O

O CR ' Cl"

O

7 i f h l ( )


18/18

7eactions of phenols (cont.)

2illiamson synthesis.+henols can be con%erted to ethers through 2illiamson synthesis.

OOHaOH#

R8 (8 5 Cl# r# 9# OSO3R)

R ' a 8

lea%age of al&yl aryl esters. 2hen al&yl aryl esters react with stron acid as H1 or H=r, the reaction

produces an al&yl halid and phenol. $he phenol does not react further to produce an aryl halide

because the carbon-oxygen bond is %ery strong, and because phenyl cations do not form readily.

OOR ' R8conc: H8# heat

H

OCH3CH3conc: Hr# heat

OCH3 H ' CH3 r

8itration, sulphonation, and riedel-rafts reactions of phenols are similar to those undergo

by arenes.

Documents

Alcohol Ett Hi Och Me Dl