18.5 Improtant web site

18. 4 Notes

18.3 Assignment

18.2 ERQs

18.1 CRQs

17.5 Improtant web site

17.4 Notes

ALCOHOL

Alcohols are hydroxy-substituted alkanes, alkenes, or alkynes in which the substitution occurs on a saturated carbon.

The general formula for alcohols is R—OH, where the R group can represent the alkyl, alkenyl, or alkynal groups. In the case of substitution on alkenes and alkynes, only saturated carbons may be substituted. For example, the following compounds are all alcohols:

If the hydroxyl group were substituted for a hydrogen on an unsaturated carbon, an alcohol would not form. For example, substituting the hydroxyl group for a terminal hydrogen of 1-propene gives an unstable enol that tautomerizes to a ketone.

Nomenclature

You can use both the common and IUPAC systems to name alcohols. In the common system, you name an alcohol by listing the alkyl group and adding the word alcohol. Following are some examples of alcohols and their common names:

In the IUPAC system, use the following series of rules to name alcohols:

1. Pick out the longest continuous chain to which the hydroxyl group is directly attached. The parent name of the alcohol comes from the alkane name for the same chain length. Drop the -e ending and add -ol.
2. Number the parent chain so that the carbon bearing the hydroxyl group has the lowest possible number. Place the number in front of the parent name.
3. Locate and name substituents other than the hydroxyl group.

The following examples show how you apply these rules:

You may classify alcohols as primary (1°), secondary (2°), or tertiary (3°), based on the class of carbon to which the hydroxyl group (—OH) is directly bonded. For example, 1-propanol is a 1° alcohol, 2-propanol is a 2° alcohol, and 2-methyl-2-propanol is a 3° alcohol.

Physical properties

Alcohols contain both a polar —OH group and a nonpolar alkyl group. As a result of this composition, alcohols that have small alkyl chains tend to be water soluble. As alkyl chain length increases, water solubility decreases.

Through the OH group, alcohols are capable of forming hydrogen bonds to themselves, other alcohols, neutral molecules, and anions. This bond formation leads to abnormally high boiling points compared to other organic molecules of similar carbon chain length.

Reference:

http://www.cliffsnotes.com/study_guide/Alcohols.topicArticleId-23297,articleId-23270.html

Oxidative Cleavage of Diols

Reaction type: Oxidation-reduction

Summary
 

1,2- or vicinal diols are cleaved by periodic acid, HIO4, into two carbonyl compounds. The reaction is selective for 1,2-diols. The reaction occurs via the formation of a cyclic periodate ester (see right). This can be used as a functional group test for 1,2-diols. The products are determined by the substituents on the diol.

Questions:
Can you recall a reaction that forms carbonyl groups via cleavage of an alkene ? 
How are 1,2-diols made from alkenes ? 
What are the oxidation states of the iodine in HIO₄ and HIO₃ ? 
 

PERIODATE CLEAVAGE OF 1,2-DIOLS
The mechanism is not trivial, so attention here is focused on the actual cleavage step. Prior to this, the alcohol reacts to form a cyclic periodate ester (shown). The periodate ester undergoes are arrangement of the electrons, cleaving the C-C bond, and forming two C=O.

Reference:

http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch15oxidativecleavagediols.html

Ester formation

Esters are compounds that are commonly formed by the reaction of oxygen-containing acids with alcohols. The ester functional group is the

Alcohols can be converted to esters by means of the Fischer Esterification Process. In this method, an alcohol is reacted with a carboxylic acid in the presence of an inorganic acid catalyst.

Because the reaction is an equilibrium reaction, in order to receive a good yield, one of the products must be removed as it forms. Doing this drives the equilibrium to the product side.

Reference:http://www.cliffsnotes.com/study_guide/Reactions-of-Alcohols.topicArticleId-23297,articleId-23272.html

Pyrolysis of sodium benzene sulfonate

In this process, benzene sulfonic acid is reacted with aqueous sodium hydroxide. The resulting salt is mixed with solid sodium hydroxide and fused at a high temperature. The product of this reaction is sodium phenoxide, which is acidified with aqueous acid to yield phenol.

Dow process

In the Dow process, chlorobenzene is reacted with dilute sodium hydroxide at 300°C and 3000 psi pressure. The following figure illustrates the Dow process.

Air oxidation of cumene

The air oxidation of cumene (isopropyl benzene) leads to the production of both phenol and acetone, as shown in the following figure. The mechanisms for the formation and degradation of cumene hydroperoxide require closer looks, which are provided following the figure.

Cumene hydroperoxide formation. The formation of the hydroperoxide proceeds by a free radical chain reaction. A radical initiator abstracts a hydrogen-free radical from the molecule, creating a tertiary free radical. The creation of the tertiary free radical is the initial step in the reaction.

In the next step, the free radical is attracted to an oxygen molecule. This attraction produces the hydroperoxide free radical.

Finally, the hydroperoxide free radical abstracts a hydrogen free radical from a second molecule of cumene to form cumene hydroperoxide and a new tertiary free radical.

Cumene hydroperoxide degradation. The degradation of the cumene hydroperoxide proceeds via a carbocation mechanism. In the first step, a pair of electrons on the oxygen of the hydroperoxide's “hydroxyl group” is attracted to a proton of the H₃O⁺ molecule, forming an oxonium ion.

Next, the oxonium ion becomes stabilized when the positively charged oxygen leaves in a water molecule. This loss of a water molecule produces a new oxonium ion.

A phenide ion shift to the oxygen atom (which creates a tertiary carbocation) stabilizes the positively charged oxygen. (A phenide ion is a phenyl group with an electron bonding pair available to form a new bond to the ring.)

The carbocation is stabilized by an acid-base reaction with a water molecule, leading to the formation of an oxonium ion.

The loss of a proton stabilizes the oxonium ion.

Next, a proton is picked up by the ether oxygen in an acid-base reaction, yielding a new oxonium ion.

The positively charged ether oxygen pulls the electrons in the oxygen-carbon bond toward itself, thus delocalizing the charge over both of the atoms. The partial positive charge on the carbon attracts the nonbonding electron pair from the oxygen of the OH group, allowing the electrons in the original oxygen-carbon bond to be released back to the more electronegative oxygen atom.

Finally, a proton is lost from the protonated acetone molecule, leading to the formation of acetone.

Ethers Ethers are alkoxy (RO—)-substituted alkanes, alkenes, and alkynes. As with alcohols, only saturated carbon atoms may be substituted in alkenes and alkynes. Nomenclature Ethers are commonly named by listing the names of the groups attached to the oxygen atom and adding the word ether. Examples include: IUPAC nomenclature names ethers as alkoxy alkanes, alkoxy alkenes, or alkoxy alkynes. The group in the chain that has the greatest number of carbon atoms is designated the parent compound. In the case of aromatic ethers, the benzene ring is the parent compound. Cyclic ethers, oxygen-containing ring systems, are normally called by their common names. Physical properties The bonds between the oxygen atom and the carbon atoms of the alkyl groups in an ether molecule are polarized due to a difference in electronegativities between carbon and oxygen. In addition, the bond angle between the alkyl groups on the oxygen is 110°. These facts show that ether molecules must be dipoles (molecules having both a center of positive and negative charge) with weak polarities. Thus, the structure of ether is similar to that of water. However, in water the hydrogen atoms have a greater partial positive charge than the hydrogen atoms on ether. In water, the charge is localized (only on) the hydrogens and not delocalized (spread throughout) as with the alkyl groups, so the charge is stronger in water than in ethers. Like water, ether is capable of forming hydrogen bonds. However, because of the delocalized nature of the positive charge on the ether molecule's hydrogen atoms, the hydrogens cannot partake in hydrogen bonding. Thus, ethers only form hydrogen bonds to other molecules that have hydrogen atoms with strong partial positive charges. Therefore, ether molecules cannot form hydrogen bonds with other ether molecules. This leads to the high volatility of ethers. Ethers are capable, however, of forming hydrogen bonds to water, which accounts for the good solubility of low molecular weight ethers in water. Table 1 shows boiling points for some simple ethers and the boiling points of alcohols of the same number of carbon atoms. Notice that due to the hydrogen bonding between alcohol molecules, all alcohols have appreciably higher boiling points than their isomeric ethers. TABLE 1 Boiling Points of Simple Ethers and Alcohols Ether Boiling Point(°C) Alcohol Boiling Point (°C) CH3OCH3 Dimethylether −25 CH3CH2OH Ethanol 79 CH3OCH2CH3 Methylethyether 11 CH3CH2CH2OH Propanol 82 CH3CH2OCH2CH3 Diethylether 35 CH3CH2CH2CH2OH Butanol 117