FRIEDEL CRAFT REACTION

Friedel-Crafts alkylation

The Friedel-Crafts reactions, discovered by French alkaloid chemist Charles Friedel and his American partner, James Crafts, in 1877, is either the alkylation or acylation of aromatic compounds catalyzed by a Lewis acid. They are very useful in the lab for formation of carbon-carbon bonds between an aromatic nucleus and a side chain.

Source of electrophile

Friedel-Crafts alkylation is an example of electrophilic substitution in aromatic compounds. The electrophile is formed in the reaction of an alkyl halide with a Lewis acid. The Lewis acid polarizes the alkyl halide molecule, causing the hydrocarbon part of it to bear a positive charge and thus become more electrophilic.

CH₃—Cl + AlCl₃ → CH₃⁺ + AlCl₄⁻

or

CH₃Cl + AlCl₃ → CH₃^δ+Cl⁺Al⁻Cl₃

(The carbon atom has a slight excess of positive charge, as the electronegative chlorine atom draws electron density towards itself. The chlorine atom has a positive charge, as it has formed a sub-ordinate bond with the aluminium atom. In effect, the Cl atom has lost an electron, while the Al atom has gained an electron. Therefore, the Al atom has a negative charge.)

Mechanism of alkylation

The polarized, electrophilic molecule then seeks to saturate its electron deficiency and forms a π-complex with the aromatic compound that is rich in π-electrons. Formation a π-complex does not lead to loss of aromaticity. The aromaticity is lost however in the σ-complex that is the next stage of reaction. The positive charge in the σ-complex is evenly distributed across the benzene ring.

C₆H₆ + CH₃⁺ → C₆H₆⁺Br → C₆H₅Br + H⁺

The σ-complex C₆H₆⁺Br can be separated (it is stable at low temperatures), while the π-complex can not.

RestrictionS

• Deactivating functional groups, such as nitro (-NO₂), usually prevent the reaction from occurring at any appreciable rate, so it is possible to use solvents such as nitrobenzene for Friedel-Crafts alkylation.

• Primary and secondary carbocations are much less stable than tertiary cations, so rearrangement typically occurs when one attempts to introduce primary and secondary alkyl groups onto the ring. Hence, Friedel-Crafts alkylation using n-butyl chloride generates the n-butylium cation, which rearranges to the t-butyl cation, which is far more stable, and the product is exclusively the t-butyl derivative. This may, in some cases, be circumvented through use of a weaker Lewis acid.

• The Friedel-Crafts reaction can not be used to alkylate compounds which are sensitive to acids, including many heterocycles.

• Another factor that restricts the use of Friedel-Crafts alkylation is polyalkylation. Since alkyl groups have an activating influence, substituted aromatic compounds alkylate more easily than the original compounds, so that the attempted methylation of benzene to give toluene often gives significant amounts of xylene and mesitylene. The usual workaround is to acylate first (see the following sections) and then reduce the carbonyl group to an alkyl group.

Friedel-Crafts acylation

Friedel-Crafts acylation, like Friedel-Crafts alkylation, is a classic example of electrophilic substitution.

Source of electrophile]Reacting with Lewis acids, anhydrides and chloranhydrides of acids become strongly polarized and often form acylium cations.

RCOCl + AlCl₃ → RC⁺O + AlCl₄^-

Mechanism of acylation                                                                                                                      The mechanism of acylation is very similar to that of alkylation.

C₆H₆ + RC⁺O → C₆H₆—CO—R + H⁺

The ketone that is formed then forms a complex with aluminum chloride, reducing its catalytic activity.

C₆H₆—CO—R + AlCl₃ → C₆H₆—C⁺(R)—O—Al⁻Cl₃

Therefore, a much greater amount of catalyst is required for acylation than for alkylation.

QUESTIONS  RELATED WITH TOPIC :

Which is most reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 2

Which is least reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 3

Which gives a meta nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 4

Which is most reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 5

Which is least reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 6

Which gives a meta nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 7

Which will be the main product upon chlorination of m-nitrotoluene with Cl2/AlCl3?

a) 

b) 

c) 

d) 

Question 8

Which is obtained as the main mononitration product upon reaction of m-t-butylanisole (1-t-butyl-3-methoxybenzene) with HNO3-H2SO4?

a) 

b) 

c) 

d) 

Question 9

Which of the following statements regarding Friedel-Crafts reactions is wrong?

a) Alkylation of benzene with an alkyl chloride requires only a catalytic amount of a Lewis acid such as aluminum chloride.

b) Alkylation of benzene with an alcohol requires only a catalytic amount of a Brønsted acid such as phosphoric acid.

c) Acetylation of benzene with acetyl chloride requires only a catalytic amount of a Lewis acid.

d) Acetylation of benzene with acetic anhydride requires more than one equivalent of a Lewis acid.

Question 10

Which of the following statements regarding electrophilic aromatic substitution is wrong?

a) Acetyl and cyano substituents are both deactivating and m-directing.

b) Alkyl groups are activating and o,p-directing.

c) Ammonio groups are m-directing but amino groups are and o,p-directing.

d) Chloro and methoxy substituents are both deactivating and o,p-directing.

Question 11

Which is most reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 12

Which is least reactive in electrophilic substitution?

a) 

b) 

c) 

d) 

Question 13

Which gives a para nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 14

Which gives a meta nitro compound as the main product upon nitration with a nitric acid-sulfuric acid mixture?

a) 

b) 

c) 

d) 

Question 15

Which of (a)-(d) does not give isopropylbenzene as a product upon reaction with benzene?

a) (CH3)2CHCl/AlCl3

b) CH3CH2CH2Cl/AlCl3

c) CH3CH=CH2/H3PO4

d) (CH3)2C=CH2/H3PO4

Question 16

Which combination of reagents used in the indicated order with benzene will give m-nitropropylbenzene?

a) 1) HNO3/H2SO4, 2) CH3CH2CH2Cl/AlCl3

b) 1) CH3CH2CH2Cl/AlCl3, 2) HNO3/H2SO4

c) 1) CH3CH2COCl/AlCl3, 2) HNO3/H2SO4, 3) H2NNH2/NaOH

d) 1) HNO3/H2SO4, 2) CH3CH2COCl/AlCl3, 3) H2NNH2/NaOH

Question 17

Which pair of compounds are the most probable main products of the following reaction?
 

a) 

b) 

c) 

d) 

Question 18

Which pair of compounds are the most probable main products of the following reaction?
 

a) 

b) 

c) 

d) 

Question 19

Which will be the main product upon bromination of phenyl benzoate with Br2/AlBr3?

a) 

b) 

c) 

d) 

Question 20

Which of the following statements regarding electrophilic aromatic substitution is wrong?

a) Sulfonation of toluene is reversible.

b) Friedel-Crafts alkylation of benzene can be reversible.

c) Friedel-Crafts alkylation with primary alkyl chloride may involve rearrangement.

d) Friedel-Crafts acylation of nitrobenzene readily gives a meta substitution product.

Completely new kind of polymer developed

Northwestern University researchers have developed a new hybrid polymer with removable supramolecular compartments, shown in this molecular model. Credit: Mark E. Seniw, Northwestern University

Imagine a polymer with removable parts that can deliver something to the environment and then be chemically regenerated to function again. Or a polymer that can lift weights, contracting and expanding the way muscles do.

"We have created a surprising new polymer with nano-sized compartments that can be removed and chemically regenerated multiple times," said materials scientist Samuel I. Stupp, the senior author of the study.These functions require polymers with both rigid and soft nano-sized compartments with extremely different properties that are organized in specific ways. A completely new hybrid polymer of this type has been developed by Northwestern University researchers that might one day be used in artificial muscles or other life-like materials; for delivery of drugs, biomolecules or other chemicals; in materials with self-repair capability; and for replaceable energy sources.

"Some of the nanoscale compartments contain rigid conventional polymers, but others contain the so-called supramolecular polymers, which can respond rapidly to stimuli, be delivered to the environment and then be easily regenerated again in the same locations. The supramolecular soft compartments could be animated to generate polymers with the functions we see in living things," he said.

Stupp is director of Northwestern's Simpson Querrey Institute for BioNanotechnology. He is a leader in the fields of nanoscience and supramolecular self-assembly, the strategy used by biology to create highly functional ordered structures.

The hybrid polymer cleverly combines the two types of known polymers: those formed with strong covalent bonds and those formed with weak non-covalent bonds, well known as "supramolecular polymers." The integrated polymer offers two distinct "compartments" with which chemists and materials scientists can work to provide useful features.

BODY ODOR AND ITS PREVENTION

Body odor, or B.O., bromhidrosis, osmidrosis and ozochrotia, is a perceived unpleasant smell our bodies can give off when bacteria that live on the skin break down sweat into acids - some say it is the smell of bacteria growing on the body, but it really is the result of bacteria breaking down protein into certain ...

People who sweat too much - those with hyperhidrosis - may also be susceptible to body odor, however, often the salt level of their sweat is too high for the bacteria to break down - it depends where the excess sweating is occurring and which type of sweat glands are involved.

Sweat itself is virtually odorless to humans; it is the rapid multiplication of bacteria in the presence of sweat and what they do (break sweat down into acids) that eventually causes the unpleasant smell. The smell is perceived as unpleasant, many believe, because most of us have been brought up to dislike it. Body odor is most likely to occur in our feet, groin, armpits, genitals, pubic hair and other hair, belly button, anus, behind the ears, and to some (lesser) extent on the rest of our skin.

Body odor can have a nice and specific smell to the individual, and can be used - especially by dogs and other animals - to identify people. Each person's unique body odor can be influenced by diet, gender, health, and medication.

Two types of acid are commonly present when there is body odor:

• Propionic acid (propanoic acid) is commonly found in sweat - propionibacteria break amino acids down into propionic acid.Propionibacteria live in the ducts of the sebaceous glands of adult and adolescent humans. Some people may identify a vinegar-like smell with propionic acid, because it is similar to acetic acid, which gives vinegar its sour taste and pungent smell.
• Isovaleric acid (3-methyl butanoic acid) is another source of body odor as a result of actions of the bacteria Staphylococcus epidermidis, which are also present in several strong cheese types.

What causes foot odor?

Most of us wear shoes and socks, making it much more difficult for the sweat to evaporate, giving the bacteria more sweat to break down into smelly substances. Moist feet also raise the risk of fungi developing, which can also give off unpleasant smells.

Apocrine glands

Apocrine glands are located in several areas, including the armpits.

These glands are found in the breasts, genital area, eyelids, armpits and ear. In the breasts they secrete fat droplets into breast milk. In the ear they help form earwax. Apocrine glands in skin and the eyelids are sweat glands.

Most of the apocrine glands in the skin are located in the groin, armpits and around the nipples of the breast. Apocrine glands in the skin usually have an odor; they are scent glands.

PREVENTION OF BODY ODOR :

TO PREVENT FOOT ODOR ALWAYS WEAR BRANDED SHOES , AND COTTON SOCKS

WHEN  YOU TAKE BATH  , ADD FEW DROPS OF LEMON JUICE 

DO YOGA DAILY , ( ANULOM VILOME )

DRINK  MORE  WATER  (  10 - 11 GLASS PER DAY )

WASH YOUR  FOOT WHEN COME AT HOME

FOR ARMS USE DEO.

THE BEST TRICK TO REMOVE BODY ODOR IS TO DO YOGA DAILY . I AM 100% SURE THAT BY DOING YOGA AYOU CAN GET FREE FROM YOUR BODY ODOR 

CHEMICAL REACTIONS IN HUMAN BODY

Roughly 96 percent of the mass of the human body is made up of just four elements: oxygen, carbon, hydrogen and nitrogen, with a lot of that in the form of water. The remaining 4 percent is a sparse sampling of the periodic table of elements. 
Some of the more prominent representatives are called macro nutrients, whereas those appearing only at the level of parts per million or less are referred to as micronutrients. 

These nutrients perform various functions, including the building of bones and cell structures, regulating the body's pH, carrying charge, and driving chemical reactions. 

The FDA has set a reference daily intake for 12 minerals (calcium, iron, phosphorous, iodine, magnesium, zinc, selenium, copper, manganese, chromium, molybdenum and chloride). Sodium and potassium also have recommended levels, but they are treated separately. 

However, this does not exhaust the list of elements that you need. Sulfur is not usually mentioned as a dietary supplement because the body gets plenty of it in proteins. 

And there are several other elements — such as silicon, boron, nickel, vanadium and lead — that may play a biological role but are not classified as essential.

"This may be due to the fact that a biochemical function has not been defined by experimental evidence," said Victoria Drake from the Linus Pauling Institute at Oregon State University.

Sometimes all that is known is that lab animals performed poorly when their diets lacked a particular non-essential element. However, identifying the exact benefit an element confers can be difficult as they rarely enter the body in a pure form.

"We don't look at them as single elements but as elements wrapped up in a compound," said Christine Gerbstadt, national spokesperson for the American Dietetic Association.

A normal diet consists of thousands of compounds (some containing trace elements) whose effects are the study of ongoing research. For now, we can only say for certain what 20 or so elements are doing. Here is a quick rundown, with the percentage of body weight in parentheses.

Oxygen (65%) and hydrogen (10%) are predominantly found in water, which makes up about 60 percent of the body by weight. It's practically impossible to imagine life without water.

Carbon (18%) is synonymous with life. Its central role is due to the fact that it has four bonding sites that allow for the building of long, complex chains of molecules. Moreover, carbon bonds can be formed and broken with a modest amount of energy, allowing for the dynamic organic chemistry that goes on in our cells.

Nitrogen (3%) is found in many organic molecules, including the amino acids that make up proteins, and the nucleic acids that make up DNA.

Calcium (1.5%) is the most common mineral in the human body — nearly all of it found in bones and teeth. Ironically, calcium's most important role is in bodily functions, such as muscle contraction and protein regulation. In fact, the body will actually pull calcium from bones (causing problems like osteoporosis) if there's not enough of the element in a person's diet.

Phosphorus (1%) is found predominantly in bone but also in the molecule ATP, which provides energy in cells for driving chemical reactions.

Potassium (0.25%) is an important electrolyte (meaning it carries a charge in solution). It helps regulate the heartbeat and is vital for electrical signaling in nerves.

Sulfur (0.25%) is found in two amino acids that are important for giving proteins their shape.

Sodium (0.15%) is another electrolyte that is vital for electrical signaling in nerves. It also regulates the amount of water in the body.

Chlorine (0.15%) is usually found in the body as a negative ion, called chloride. This electrolyte is important for maintaining a normal balance of fluids.

Magnesium (0.05%) plays an important role in the structure of the skeleton and muscles. It also is necessary in more than 300 essential metabolic reactions.

Iron (0.006%) is a key element in the metabolism of almost all living organisms. It is also found in hemoglobin, which is the oxygen carrier in red blood cells. Half of women don't get enough iron in their diet. 

Fluorine (0.0037%) is found in teeth and bones. Outside of preventing tooth decay, it does not appear to have any importance to bodily health.

Zinc (0.0032%) is an essential trace element for all forms of life. Several proteins contain structures called "zinc fingers" help to regulate genes. Zinc deficiency has been known to lead to dwarfism in developing countries. 

Copper (0.0001%) is important as an electron donor in various biological reactions. Without enough copper, iron won't work properly in the body.

Iodine (0.000016%) is required for making of thyroid hormones, which regulate metabolic rate and other cellular functions. Iodine deficiency, which can lead to goiter and brain damage, is an important health problem throughout much of the world.

The most significant chemical reactions

Metabolic pathways in human organism form vast network of more or less interconnected reactions that often share common intermediate products. Chemical conversions, which occur during the chemical reactions, can be divided according to the general mechanism, shared by all substances undergoing that particular reaction. For example, decarboxylationreactions involve splitting off a CO2 molecule from the carboxyl group and its substrates include various carboxylic acids.

In this subchapter, we will speak about the most important types of chemical reactions with typical examples taken from human metabolic pathways.

Alcohols, carbonyl compounds and carboxylic acids

Alcohols, carbonyl compounds and carboxylic acids form an important group of substances involved in many chemical reactions of intermediate metabolism.

Alcohols are characterized by the presence of OH- functional group. Depending on the number of these groups in the molecule, alcohols can by mono-, di- or polyhydric. Another division is based on the nature of a carbon atom to which an OH- group is attached: primary(R-CH2-OH), secondary (R1-CH(OH)-R2) and tertiary (C-R1R2R3(OH)) alcohols.

Aldehydes and ketones together, for a group of carbonyl compounds. Their functional groups are –CHO and C=O, respectively.

Carboxylic acids, characterised by the presence of –COOH group, and their derivatives are probably the most important members of this group of substances.

Alcohols, carbonyl compounds and carboxylic acids participate in many reactions – among the most significant are:

1) The formation of anions and acyls, derived from carboxylic acids

2) Dehydrogenations and hydrogenations (oxidations and reductions)

3) Esterifications

1) The formation of anions and acyls, derived from carboxylic acids

Carboxyl group is capable of dissociation, the extent of which, for a particular acid, is expressed by dissociation constant. In general, carboxylic acids belong to weak acids, which means that they dissociate only partially. The resulting anion (with -COO- group) is termedacetate.

After splitting off the OH- group from carboxyl an acyl is formed.

2) Dehydrogenations and hydrogenations (oxidations and reductions)

Dehydrogenation is a chemical reaction leading to the elimination of –H atom from the molecules. The hydrogen atom obtained in this process can be subsequently used to create a proton gradient across the mitochondrial membrane in order to gain energy (ATP). The incorporation of the hydrogen into the molecule is termed hydrogenation. Hydrogenations and dehydrogenations occur during:

a) The oxidation of simple bonds to double bonds

b) The reciprocal conversions of alcohols – carbonyl compounds – carboxylic acids

a) The oxidation of simple bonds to double bonds

The general reaction scheme is as follows:

-CH2-CH2- ↔ -CH=CH- + 2H+ + 2e-

Such reactions are abundant in Krebs cycle, β-oxidation of fatty acids or desaturation reactions (producing unsaturated fatty acids).

b) The reciprocal conversions of alcohols – carbonyl compounds – carboxylic acids

This threesome of organic compounds forms a series that differ in the degree of oxidation(or reduction). General scheme of their interconversion is as follows (conversion towards the carbonyl compound and carboxylic acid is oxidation, in opposite direction it is a reduction):

1. Primary alcohol ↔ aldehyde ↔ carboxylic acid

R-CH2-OH ↔ R-CHO ↔ R-COOH

2. Secondary alcohol ↔ ketone

R1-CH(OH)-R2 ↔ R1-CO-R2

3. Tertiary alcohol – cannot be oxidised

As an example of oxidation, we can take the conversion of glycerol-3-phosphate todihydroxyacetone phosphate (DHA-P), with FAD as a cofactor, through which a glycerol enters the metabolic pathways of glycolysis or gluconeogenesis (depending on the actual needs of the organism).

3) Esterification

Esterification is a reaction between carboxylic acid and alcohol, creating an ester and awater molecule:

R1-OH + R-COOH → R1-O-(C=O)-R + H2O