01:160:307 Lecture Notes - Lecture 11: Oxidation State, Electronegativity, Hydrogenation

21 views15 pages

champagnesnake948

29 Dec 2019

School

Department

Course

Professor

For unlimited access to Class Notes, a Class+ subscription is required.

Chapter 11 – Oxidation Reduction Reaction (307 Fall 2019) Page 1

Chapter 11: Oxidation and Reduction Reaction

1. Oxidation and Reduction – definition

2. Catalytic hydrogenation

3. Oxidation reaction of alkenes

4. Oxidation reaction of alcohols

5. Oxidation reaction of amines

1. Oxidation and Reduction – definition

Increase in oxidation number of an atom on the product side is oxidation or and

decrease in oxidation number of an atom on the product side is reduction.

Example:

In organic molecules, oxidation involves a carbon atom to gain bonds to more

electronegative elements, most commonly oxygen. Reduction involves a carbon atom

gains bonds to less electronegative elements, most commonly hydrogen.

Unlock document

This preview shows pages 1-3 of the document.
Unlock all 15 pages and 3 million more documents.

Already have an account? Log in

Chapter 11 – Oxidation Reduction Reaction (307 Fall 2019) Page 2

2. Catalytic Hydrogenation (Reduction)

a. Catalytic hydrogenation of alkenes

Catalytic hydrogenation of alkenes produces corresponding alkanet the reaction requires

a metal catalyst, usually Pt, Pd, or Ni, and the mechanism involves absorption of hydrogen

to the metal surface followed by absorption of alkenes (heterogeneous catalysis)

• palladium is obtained commercially “supported” on an inert substance, such as

charcoal, (Pd/C). The alkene is usually dissolved in ethanol when Pd/C is used

as the catalyst.

• platinum is used as PtO2, Adams’ catalyst, although it is actually platinum metal

that is the catalyst. Ethanol or acetic acid is used as the solvent for the alkene.

General reaction:

i) It is a syn addition reaction and the reaction is stereoselective.

ii) Catalytic hydrogenation is chemoselective. Other types of compounds containing

multiple bonds, such as ketones, esters, and nitriles, do not react with hydrogen under

the conditions used to hydrogenate alkenes. The examples below show reduction of an

alkene, but the ketone and carboxylic acid groups present remain intact and are not

reduced. Aromatic rings are also not reduced under the conditions used to reduce

alkenes

Unlock document

This preview shows pages 1-3 of the document.
Unlock all 15 pages and 3 million more documents.

Already have an account? Log in

Chapter 11 – Oxidation Reduction Reaction (307 Fall 2019) Page 3

iii) Heat of hydrogenation (negative) can be used to measure relative stability of alkene

II is more stable than I by 3.4 kcal/mol. More the number of alkyl groups around (C=C)

bond, lower the heat of hydrogenation (lesser exothermic or lesser negative), more the

stability. Trans isomers are more stable than cis.

Order of Stability:

Rankstability1leastexothermicto moltexothermic

onexam Ok DE

Unlock document

This preview shows pages 1-3 of the document.
Unlock all 15 pages and 3 million more documents.

Already have an account? Log in

Document Summary

Chapter 11: oxidation and reduction reaction: oxidation and reduction definition, catalytic hydrogenation, oxidation reaction of alkenes, oxidation reaction of alcohols, oxidation reaction of amines, oxidation and reduction definition. Increase in oxidation number of an atom on the product side is oxidation or and decrease in oxidation number of an atom on the product side is reduction. In organic molecules, oxidation involves a carbon atom to gain bonds to more electronegative elements, most commonly oxygen. Reduction involves a carbon atom gains bonds to less electronegative elements, most commonly hydrogen. Page 1: catalytic hydrogenation (reduction, catalytic hydrogenation of alkenes. The alkene is usually dissolved in ethanol when pd/c is used as the catalyst: platinum is used as pto2, adams" catalyst, although it is actually platinum metal that is the catalyst. Ethanol or acetic acid is used as the solvent for the alkene. General reaction: it is a syn addition reaction and the reaction is stereoselective, catalytic hydrogenation is chemoselective.

Related Questions

Â¥Write a brief (less than 150 words, 3 or 4 sentences) of the aim of the experiment

Â¥Address question of what was done, how it was done, and what compounds were used.

Â¥Include Chemical Reaction where relevant.

See text below. Please provide Purpose following the steps above. Thank you.

Alcohols R-O-H are characterized by the presence of the hydroxyl group

Because of intermolecular co-association, alcohols show higher boiling points

than aldehydes, ethers, or ketones of similar mass. Among alcohols, boiling

points increase with increased surface area. Increased surface area occurs as

more carbons are added to the alkyl portion or with decreased branching of th

alkyl group. Thus, 1-propanol has a higher boiling point than ethanol

(increased C#). 1-propanol also has a higher boiling point than 2-propanol

(decreased branching)

The solubility of alcohols in water decreases as the surface area of the

alkyl (nonpolar) portion increases. Thus, alcohols become less soluble in water

as the number of carbons in the alkyl group increases. When comparing

alcohols that contain the same number of carbons, branching of the alkyl group

decreases its surface area and thus increases the water solubility of the alcohol.

1-Propanol is slightly soluble in water while 2-propanol is quite soluble

The limit of water solubility is reached at about 4 or 5 carbons in the

alkyl group. However, it is possible to "salt out" or separate a water-soluble

alcohol from the water it is mixed with by the addition of certain salts such as

K2CO3. If an alcohol-water mixture is saturated with such a salt, the anion

selectively forms strong ion-dipole bonds to water, leaving the alcohol as a

separate layer. Thus, water is separated from the alcohol because the ionic salt

bonds more strongly with water than with the alcohol. There are twice as many

ion-dipole bonds possible with water than with the alcohol.

Alcohols are relatively acidic organic molecules, being weaker acids than

water, yet stronger than acetylene.

Acidity: water > alcohol > acetylene > ammonia > alkanes

Alcohols may be converted to sodium alkoxides by the action of metallic sodium

under anhydrous conditions. Primary alcohols react more readily tharn

secondary or tertiary alcohols due to the relative stability of the alkoxide ions in

the solvent alcohol.

R-o:-

Alcohols undergo nucleophilic substitution reactions with ease under

acidic conditions. The relative ease of such substitution for primary, secondary

and tertiary alcohols serves as a means of classification. Upon treatment with

concentrated HC1, tertiary alcohols are rapidly converted to alkyl chlorides

Secondary alcohols require warming in a boiling water bath for 15 minutes

Primary alcohols do not react at all under these conditions. The alkyl chlorides

formed by this reaction are insoluble in the concentrated HCl and form an

easily detectable second layer

R-O-H HC1 >

Ð-Ð-Ð

Complications arise from the fact that benzylic and allylic alcohols also

react immediately, but yield products that are soluble in the concentrated HCI

Alcohols are easily oxidized by any of these strong oxidizing agents:

dilute KMnO4, NajCr.07 in acid, or CrO3 (chromic anhydride)

acidified sodium dichromate is somewhat helpful in the classification of

alcohols. Prim

ary and secondary alcohols are oxidized rapidly within several

minutes, while tertiary alcohols do not react under these conditions

Oxidation occurs more easily when the carbon bearing the -OH group

bonded to at least one atom of hydrogen. The complex mechanism of

involves the transfer of a hydride ion H:- as a critical step.

hydrogen atom is absent (as in tertiary alcohols), no oxidation can occur

directly. Tertiary alcohols may be oxidized indirectly through the formation of

Alcohols which contain the partial structure C- CH3 give positive

Ð¾Ð½

results in the iodofora reaction. When the alcohol is dissolved in water and

KOH, the addition of a solution of 12 in KI yields a yellow precipitate of

iodoform, CHI3, along with the oxidized portion of the alcohol

Hypoiodite ion is produced by the reaction between molecular iodine and

hydroxide ion:

I2 + 4(OH) -

The hypoiodite ion in turn oxidizes an alcohol with the proper structure

Once this oxidation has occurred, additional hypoiodite ion continues to

react with the aldehyde or ketone produced:

CH,-C

3 (0I)-IC-c3 (OH)-

resulting in the final substitution reaction to give iodoform and the anion of a

carboxylic acid containing one carbon atom less than the original alcohol:

128

lodoform precipitates as fine yellow crystals. This precipitate, a result of a

specific oxidation followed by a substitution, is an indication of the partial

structure of the original alcohol.

Simple alcohols of up to ten carbon atoms may be detected by the

ammonium hexanitrocerrata(lV) reagent, (NH4Ce(NO,). The hexanitro-

cerrate(IV) ion has a distinctive orange-red color. When an alcohol, ROH is

added, one or more OR- groups replace the nitro groups as ligands in the

complex ion. The new complex ion formed has a distinctive color. The general

equation for this reaction is:

This test is positive for aliphatic alcohols up to approximately ten carbons in

length. Phenols or larger alcohols yield insoluble mixtures

Alcohols react with acids or with acid derivatives to form esters. This

characteristic reaction is useful in the formation of specific esters such as ethyl

acetate, acetylsalicylic acid (aspirin) and methyl salicylate (oil of wintergreen). In

this experiment, methyl salicylate will be prepared by reacting methyl alcohol

with salicylic acid in the presence of a trace of sulfuric acid as the catalyst

Lower molecular weight alcohols such as ethanol, methanol, and

isopropyi alcohol absorb water on exposure to moist air or are prepared as

azeotropic mixtures containing water. The presence of water in alcohols may be

detected in several ways. If a small lump of CaC2 is added to any alcohol that

contains a trace of water, a reaction occurs that produces immediate bubbles of

acetylene gas:

Thus, evolution of acetylene gas upon the addition of calcium carbide indicates

the presence of water in the alcohol. Another way to test for the presence of

water in alcohols involves the use of anhydrous cupric sulfate powder (CuSO4)

Anhydrous cupric sulfate is a very pale, almost white powder. In the presence of

water, deep blue crystals of cupric sulfate pentahydrate,

CuSO4-5H20, are formed. Thus, anhydrous cupric sulfate indicates the

presence of water in an alcohol by a simple color change.

Commercial ethanol is produced as an azeotropic mixture that contains

95% ethanol and 5% water. Absolute alcohol contains no water. Many reagent

grade alcohols are composed of a nonpotable mixture of 95% ethanol and 5%

isopropyl alcohol. Thus, absolute ethanol and reagent alcohols are both water

free and give negative results when tested for the presence of water

For each of the following, fill in the blank with the correct response. All of these fill-in-the-blank problems pertain to material covered in the sections on alkanes, alkenes and alkynes, aromatic hydrocarbons, and hydrocarbon derivatives.

a. The first "organic" compound to be synthesized in the laboratory, rather than being isolated from nature, was _ _ _ _ _, which was prepared from _ _ _ _ _.

b. An organic compound whose carbon-carbon bonds are all single bonds is said to be _ _ _ _ _.

c. The general orientation of the four pairs of electrons around the carbon atoms in alkanes is _ _ _ _ _.

d. Alkanes in which the carbon atoms form a single unbranched chain are said to be _ _ _ _ _ alkanes.

e. Structural isomerism occurs when two molecules have the same number of each type of atom but exhibit a different arrangement of the _ _ _ _ _ between those atoms.

f. The systematic names of all saturated hydrocarbons have the ending _ _ _ _ _ added to a root name that indicates the number of carbon atoms in the molecule.

g. For branched hydrocarbon, the root name for the hydrocarbon comes from the number of carbon atoms in the _ _ _ _ _ continuous chain in the molecule.

h. The positions of substituents along the hydrocarbon framework of a molecule are indicated by the _ _ _ _ _ of the carbon atom to which the substituents are attached.

i. The major use of alkanes has been in _ _ _ _ _ reactions, as a source of heat and light.

j. With very reactive agents, such as the halogen elements, alkanes undergo _ _ _ _ _ reactions, whereby a new atom replaces one or more hydrogen atoms of the alkane.

k. Alkenes and alkynes are characterized by their ability to undergo rapid, complete _ _ _ _ _ reactions, by which other atoms attach themselves to the carbon atoms of the double or triple bond.

l. Unsaturated fats may be converted to saturated fats by the process of _ _ _ _ _.

m. Benzene is the parent member of the group of hydrocarbons called _ _ _ _ _ hydrocarbons.

n. An atom or group of atoms that imparts new and characteristic properties to an organic molecule is called a _ _ _ _ _ group.

o. A _ _ _ _ _ alcohol is one in which there is only one hydrocarbon group attached to the carbon atom holding the hydroxyl group.

p. The simplest alcohol, methanol, prepared industrially by the hydrogenation of _ _ _ _ _.

q. Ethanol is commonly prepared by the _ _ _ _ _ of certain sugars by yeast.

r. Both aldehydes and ketones contain the _ _ _ _ _ group, but they differ in where this group occurs along the hydrocarbon chain.

s. Aldehydes and ketones can be prepared by _ _ _ _ _ of the corresponding alcohol.

t. Organic acids, which contain the _ _ _ _ _ group, are typically weak acids.

u. The typical sweet-smelling compounds called _ _ _ _ _ result from the condensation reaction of organic acid with an _ _ _ _ _.

rubyzebra85

01:160:307 Lecture Notes - Lecture 11: Oxidation State, Electronegativity, Hydrogenation

Document Summary

Get access

Related Documents

01:160:307 Lecture Notes - Lecture 19: Electrophilic Addition, Sigmatropic Reaction, Halogenation

01:160:307 Chapter 6: Lesson Plan 6

CHEM 2311 Lecture Notes - Lecture 16: Heterogeneous Catalysis, Syn And Anti Addition, Saturated And Unsaturated Compounds

Related Questions