# Organic Chemistry/Alcohols

**Alcohols** are the family of compounds that contain one or more
**hydroxyl (-OH)** groups attached to a single bonded alkane. Alcohols
are represented by the general formula -OH. Alcohols are important in
organic chemistry because they can be converted to and from many other
types of compounds. Reactions with alcohols fall into two different
categories. Reactions can cleave the R-O bond or they can cleave the O-H
bond.

Ethanol (ethyl alcohol, or grain alcohol) is found in alcoholic
beverages, CH~3~CH~2~OH.

# Preparation

In the Alkenes section, we
already covered a few methods for synthesizing alcohols. One is the
hydroboration-oxidation of alkenes and the other is the
oxymercuration-reduction of alkenes. But there are a great many other
ways of creating alcohols as well.

A common source for producing alcohols is from carbonyl compounds. The
choice of carbonyl type (ketone, aldehyde, ester, etc.) and the type of
reaction (Grignard addition or Reduction), will determine the product(s)
you will get. Fortunately, there are a number of variations of
carbonyls, leading to a number of choices in product.

There are primarily two types of reactions used to create alcohols from
carbonyls: Grignard Addition reactions and Reduction reactions. We\'ll
look at each type of reaction for each type of carbonyl.

### Grignard Addition Reactions

As we learned previously, Grignard
reagents
are created by reacting magnesium metal with an alkyl halide (aka
haloalkanes). The magnesium
atom then gets between the alkyl group and the halogen atom with the
general reaction:

R-X + Mg → R-Mg-X

In our examples, we\'ll be using bromine in our Grignard reagents
because it\'s a common Grignard halogen and it will keep our examples a
little clearer without the need for X.

!Mechanism of Grignard reagent reacting with a
carbonyl{width="600"}

The general mechanism of a Grignard reagent reacting with a carbonyl
(except esters) involves the creation of a 6-membered ring transition
state. The pi bond of the oxygen attacks a neighboring magnesium bromide
which in turn, releases from its R group leaving a carbocation. At the
same time, the magnesium bromide ion from another Grignard molecule is
attacked by the carbocation and has its magnesium bromide ion stolen
(restoring it to its original state as a Grignard reagent). The second
molecule\'s carbocation is then free to attack the carbanion resulting
from the vacating pi bond, attaching the R group to the carbonyl.

According to youtube, see Grignard reagent, the carbanion (R:-) from the
R-MgBr attacks the partially positive carbonyl carbon, displacing the pi
electrons onto the O, which takes a proton, forming the alcohol.

At this point, there is a magnesium bromide on the oxygen of what was a
carbonyl. The proton from the acidic solvent easily displaces this
magnesium bromide ion and protonates the oxygen, creating a primary
alcohol with formaldehyde, a secondary alcohol with an aldehyde and a
tertiary alcohol with a ketone.

With esters, the mechanism is slightly different. Two moles of Grignard
are required for each mole of the ester. Initially, the pi bond on the
carbonyl oxygen attacks the magnesium bromide ion. This opens up the
carbon for attack from the R group of the Grignard. This part of the
reaction is slow because of the dual oxygens off of the carbon providing
some resonance stabilization. The oxygen\'s pi bond then re-forms,
expelling the O-R group of the ester which then joins with the magnesium
bromide, leaving R-O-MgBr and a ketone. The R-O-MgBr is quickly
protonated from the acidic solution and the ketone is then attacked by
Grignard reagent via the mechanism described earlier.

#### Synthesis from Formaldehyde

!Synthesis of alcohol from formaldehyde and Grignard
reagent{width="600"}

The image above shows the synthesis of an alcohol from formaldehyde
reacted with a Grignard reagent. When a formaldehyde is the target of
the Grignard\'s attack, the result is a primary alcohol.

#### Synthesis from an Aldehyde

!Synthesis of alcohol from an aldehyde and Grignard
reagent{width="600"}

The image above shows the synthesis of an alcohol from an aldehyde
reacted with a Grignard reagent. When an aldehyde is the target of the
Grignard\'s attack, the result is a secondary alcohol.

#### Synthesis from a Ketone

!Synthesis of alcohol from an ketone and Grignard
reagent{width="600"}

The image above shows the synthesis of an alcohol from a ketone reacted
with a Grignard reagent. When a ketone is the target of the Grignard\'s
attack, the result is a tertiary alcohol.

#### Synthesis from an Ester

!Synthesis of alcohol from an ester and Grignard
reagent{width="600"}

The image above shows the synthesis of an alcohol from an ester reacted
with a Grignard reagent. When an ester is the target of the Grignard\'s
attack, the result is a tertiary alcohol and a primary alcohol. The
primary alcohol is always from the -O-R portion of the ester and the
tertiary alcohol is the other R groups of the ester combined with the R
group from the Grignard reagent.

#### Synthesis from an Epoxide

!Synthesis of alcohol from an epoxide and Grignard
reagent{width="600"}

We will discuss reactions with Epoxides later when we cover epoxides,
but for now, we\'ll briefly discuss the synthesis of an alcohol from an
epoxide. The nature of the reaction is different than with the
carbonyls, as might be expected. The reaction of Grignard reagents with
epoxides is regioselective. The Grignard reagent attacks at the least
substituted side of the carbon-oxygen bonds, if there is one. In this
case, one carbon has 2 hydrogens and the other has 1, so the R group
attacks the carbon with 2 hydrogens, breaking the bond with oxygen which
is then protonated by the acidic solution. leaving a secondary alcohol
and a concatenated carbon chain. The R group can be alkyl or aryl.

#### Organolithium Alternative

As an alternative to Grignard reagents, organolithium reagents can be
used as well. Organolithium reagents are slightly more reactive, but
produce the same general results as Grignard reagents, including the
synthesis from epoxides. IT IS KNOWN AS Organolithium Alternative.

### Reduction

#### Synthesis from an Aldehyde

!Synthesis of alcohol from an aldehyde by
reduction.{width="600"}

The image above shows the synthesis of an alcohol from an aldehyde by
reduction.

#### Synthesis from a Ketone

!Synthesis of alcohol from an aldehyde by
reduction{width="600"}

The image above shows the synthesis of an alcohol from a ketone by
reduction.

#### Synthesis from an Ester

!Synthesis of alcohol from an ester by
reduction{width="600"}

The image above shows the synthesis of an alcohol from an ester by
reduction. Esters can be hydrolysed to form an alcohol and a carboxylic
acid.

#### Synthesis from a Carboxylic Acid

!Synthesis of alcohol from a carboxylic acid by
reduction{width="600"}

The image above shows the synthesis of an alcohol from a carboxylic acid
reacted by reduction.

# Properties

## Naming alcohols

Follow these rules to name alcohols the IUPAC way:

1.  find the longest carbon chain containing at least one OH group, this
    is the parent
    1.  if there are multiple OH groups, look for the chain with the
        most of them, and the way to count as many carbons in that chain
    2.  name as an alcohol, alkane diol, triol, etc.
2.  number the OH groups, giving each group the lowest number possible
    when different numbering possibilities exist
3.  treat all other groups as lower priority substituents (alcohol /
    hydroxy groups are the highest priority group for naming)

### Example alcohols

                                                                                    IUPAC name                                         Common name
  --------------------------------------------------------------------------------- -------------------------------------------------- -------------------------------------------------------------------------------------------------
  CH~3~CH~2~OH                                                                      Ethanol                                            Ethyl alcohol
  CH~3~CH~2~CH~2~-OH                                                                1-Propanol                                         n-Propyl alcohol
  (CH~3~)~2~CH-OH                                                                   2-Propanol                                         Isopropyl alcohol (Note: Isopropanol would be incorrect. Cannot mix and match between systems.)
                                                                                    2-Ethylbutan-1-ol                                  2-Ethylbutanol
                                                                                    3-Methyl-3-pentanol                                
                                                                                    2,2-Dimethylcyclopropanol                          
  Multiple OH functional groups                                                                                                        
                                                                                    1,2-Ethanediol                                     Ethylene glycol
                                                                                    1,1-Ethanediol                                     Acetaldehyde hydrate
                                                                                    1,4-Cyclohexanediol                                
  (form that body fat is stored as)                                                 1,2,3-Propanetriol                                 Glycerol
  ^-^OH can be named as a substituent hydroxyl group (hydroxyalkanes)                                                                  
                                                                                    1,2-Di(hydroxymethyl)cyclohexane                   
                                                                                    2-(hydroxymethyl)-1,3-propanediol                  
  Find the longest chain of carbons containing the maximum number of ^-^OH groups                                                      
                                                                                    1-(1-hydroxyethyl)-1-methylcyclopropane            
                                                                                    2-(1-methylcyclopropyl)ethanol                     
                                                                                    2-(2-hydroxyethyl)-2-methylcyclopropanol           
                                                                                    3-(2-hydroxyethyl)-3-methyl-1,2-cyclopropanediol   

## Acidity

In an O-H bond, the O steals the H\'s electron due to its
electronegativity, and O can carry a negative charge (R-O^-^). This
leads to **deprotonation** in which the nucleus of the H, a proton,
leaves completely. This makes the -OH group (and alcohols) Bronsted
acids. Alcohols are weak acids, even weaker than water. Ethanol has a
pKa of 15.9 compared to water\'s pKa of 15.7. The larger the alcohol
molecule, the weaker an acid it is.

On the other hand, alcohols are also weakly basic. This may seem to be
contradictory\--how can a substance be both an acid and a base? However,
substances exist that can be an acid or a base depending on the
circumstances. Such a compound is said to be amphoteric or amphiprotic.
As a Bronsted base, the oxygen atom in the -OH group can accept a proton
(hydrogen ion.) This results in a positively-charged species known as an
oxonium ion. Oxonium ions have the general formula ROH~2~^+^, where R is
any alkyl group that is a carbon containing species that ranges from
-CH3.

## Alkoxides

When O becomes deprotonated, the result is an **alkoxide**. Alkoxides
are anions. The names of alkoxides are based on the original molecule.
(Ethanol=ethoxide, butanol=butoxide, etc.) Alkoxides are good
nucleophiles due to the negative charge on the oxygen atom.

### Producing an alkoxide

R-OH -\> H^+^ + R-O^-^

In this equation, R-O^-^ is the alkoxide produced and is the conjugate
base of R-OH

Alcohols can be converted into alkoxides by reaction with a strong base
(must be stronger than OH^-^) or reaction with metallic sodium or
potassium. Alkoxides themselves are basic. The larger an alkoxide
molecule is, the more basic it is.

# Reactions

## Conversion of alcohols to haloalkanes

Recall that haloalkanes can be converted to alcohols through
nucleophilic substitution.

+------------------------------------------+
| ```{=html}                               |
| <H2>                                     |
| ```                                      |
| Conversion of a haloalkane to an alcohol |
|                                          |
| ```{=html}                               |
| </H2>                                    |
| ```                                      |
| R-X + OH^-^ → R-OH + X^-^                |
+------------------------------------------+

This reaction proceeds because X (a halogen) is a good leaving group and
OH^-^ is a good nucleophile. OH, however, is a poor leaving group. To
make the reverse reaction proceed, OH must become a good leaving group.
This is done by protonating the OH, turning it into H~2~O^+^, which is a
good leaving group. H^+^ must be present to do this. Therefore, the
compounds that can react with alcohols to form haloalkanes are HBr, HCl,
and HI. Just like the reverse reaction, this process can occur through
S~N~2 (backside attack) or S~N~1 (carbocation intermediate) mechanisms.

+--------------------------------------------------------+
| ```{=html}                                             |
| <H2>                                                   |
| ```                                                    |
| S~N~2 conversion of an alcohol to a haloalkane         |
|                                                        |
| ```{=html}                                             |
| </H2>                                                  |
| ```                                                    |
| R-O-H + H^+^ + X^-^ → R-O^+^-H~2~ + X^-^ → R-X + H~2~O |
+--------------------------------------------------------+

+----------------------------------------------------------------------+
| ```{=html}                                                           |
| <H2>                                                                 |
| ```                                                                  |
| S~N~1 conversion of an alcohol to a haloalkane                       |
|                                                                      |
| ```{=html}                                                           |
| </H2>                                                                |
| ```                                                                  |
| R-O-H + H^+^ + X^-^ → R-O^+^-H~2~ + X^-^ → R^+^ + H~2~O + X^-^ →     |
| R-X + H~2~O                                                          |
+----------------------------------------------------------------------+

As stated in the haloalkane chapter, the two mechanisms look similar but
the mechanism affects the rate of reaction and the stereochemistry of
the product.

## Oxidation of alcohols

Oxidation in organic chemistry always involves either the addition of
oxygen atoms (or other highly electronegative elements like sulphur or
nitrogen) or the removal of hydrogen atoms. Whenever a molecule is
oxidized, another molecule must be reduced. Therefore, these reactions
require a compound that can be reduced. These compounds are usually
inorganic. They are referred to as *oxidizing reagents*.

With regards to alcohol, oxidizing reagents can be strong or weak. Weak
reagents are able to oxidize a primary alcohol group into a aldehyde
group and a secondary alcohol into a ketone. Thus, the R-OH (alcohol)
functional group becomes R=O (carbonyl) after a hydrogen atom is
removed. Strong reagents will further oxidize the aldehyde into a
carboxylic acid (COOH). Tertiary alcohols cannot be oxidized.

An example of a strong oxidizing reagent is chromic acid (H~2~CrO~4~).
Some examples of a weak oxidizing reagents are pyridinium chlorochromate
(PCC) (C~5~H~6~NCrO~3~Cl) and pyridinium dichromate (PDC).


------------------------------------------------------------------------

\<\< Haloalkanes \| Alcohols
\| Alkenes \>\>

id:Kimia Organik/Alkohol
