example and uses of alkyl halides
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- "Alkylating agent" redirects here. For the class of drugs, seealkylating antineoplastic agent.
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbene (or their equivalents) . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in organic molecules. Many biological target molecules or their synthetic precursors are composed of an alkyl chain with specific functional groups in a specific order. Selective alkylation, or adding parts to the chain with the desired functional groups, is used, especially if there is no commonly available biological precursor. Alkylation with only one carbon is termed methylation.
Nucleophilic alkylating agents
Nucleophilic alkylating agents deliver the equivalent of an alkyl anion (carbanion). Examples include the use of organometallic compounds such as Grignard (organomagnesium), organolithium, organocopper, and organosodium reagents. These compounds typically can add to an electron-deficient carbon atom such as at a carbonyl group. Nucleophilic alkylating agents can also displace halide substituents on a carbon atom. In the presence of catalysts, they also alkylate alkyl and aryl halides, as exemplified by Suzuki couplings.
Electrophilic alkylating agents
Electrophilic alkylating agents deliver the equivalent of an alkylcation. Examples include the use of alkyl halides with a Lewis acid catalyst to alkylate aromatic substrates in Friedel-Crafts reactions. Alkyl halides can also react directly with amines to form C-N bonds; the same holds true for other nucleophiles such as alcohols, carboxylic acids, thiols, etc.
Electrophilic, soluble alkylating agents are often very toxic, due to their ability to alkylate DNA. They should be handled with proper PPE. This mechanism of toxicity is also responsible for the ability of some alkylating agents to perform as anti-cancer drugs in the form of alkylating antineoplastic agents, and also as chemical weapons such as mustard gas. Alkylated DNA either does not coil or uncoil properly, or cannot be processed by information-decoding enzymes. This results in cytotoxicity with the effects of inhibition the growth of the cell, initiation of programmed cell death or apoptosis. However, mutations are also triggered, including carcinogenic mutations, explaining the higher incidence of cancer after exposure.
- R-OH + R'-X â†’ R-O-R' + H-X
The produced acid HX is removed with a base, or, alternatively, the alcohol is deprotonated first to give an alkoxide or phenoxide. For example, dimethyl sulfate alkylates the sodium salt of phenol to give anisole, the methyl ether of phenol. The dimethyl sulfate is dealkylated to sodium methylsulfate.
- Ph-Oâ€“ Na+ + Me2SO4â†’ Ph-O-Me + Na+ MeSO4â€“
On the contrary, the alkylation of amines introduces the problem that the alkylation of an amine makes it more nucleophilic. Thus, when an electrophilic alkylating agent is introduced to a primary amine, it will preferentially alkylate all the way to a quaternary ammonium cation.
- R-NH2â†’ R-NH-R' â†’ R-N(R')2â†’ R-N(R')3+ (alkylating agent omitted for clarity)
If the quaternary ammonium is not th
If the acid is a carboxylic acid, the compound contains a â€“COXfunctional group, which consists of a carbonyl group singly bonded to a halogen atom. The general formula for such an acyl halide can be written RCOX, where R may be, for example, an alkyl group, CO is the carbonyl group, and X represents the halide, such as chloride. Acyl chlorides are the most commonly encountered acyl halides, but acetyl iodide is the one produced (transiently) on the largest scale. Billions of kilograms are generated annually in the production of acetic acid.
A common laboratory method for the synthesis of acyl halides entails reaction of carboxylic acids with reagents such as thionyl chloride or phosphorus pentachloride for acyl chlorides, phosphorus pentabromide for acyl bromides and cyanuric fluoride for acyl fluorides.
Acyl halides are rather reactive compounds often synthesized to be used as intermediates in the synthesis of other organic compounds. For example, an acyl halide can react with:
- water, to form a carboxylic acid. This hydrolysis is the most heavily exploited reaction for acyl halides as it occurs in the industrial synthesis of acetic acid.
- an aromatic compound, using a Lewis acid catalyst such as AlCl3, to form an aromatic ketone. SeeFriedel-Crafts acylation.
Multiple functional groups
A molecule can have more than one acyl halide functional group. For example, "adipoyl dichloride", usually simply called adipoyl chloride, has two acyl chloride functional groups; see the structure at right. It is the dichloride (i.e., double chloride) of the 6-carbon dicarboxylic acid adipic acid. An important use of adipoyl chloride is polymerization with an organic di-amino compound to form a polyamide called nylon or polymerization with certain other organic compounds to form polyesters.
Phosgene (carbonyl dichloride, Clâ€“COâ€“Cl) is a very toxic gas that is the dichloride of carbonic acid (HOâ€“COâ€“OH). Both chloride radicals in phosgene can undergo reactions analogous to the preceding reactions of acyl halides. Phosgene is used a reactant in the production of polycarbonate polymers, among other industrial applications.
Volatile acyl halides are lachrymatory because they can react with water at the surface of the eye producing hydrohalic and organic acids irritating to the eye. Similar problems can result if one inhales acyl halide vapors. In general, acyl halides (even non-volatile compounds such as tosyl chloride) are irritants to the eyes, skin and mucous membranes.
The first few members of the series are volatile liquids; methyl nitrite and ethyl nitrite are gaseous at room temperature and pressure. The compounds have a distinctive fruity odor. Another frequently encountered nitrite is amyl nitrite (3-methylbutyl nitrite).
Alkyl nitrites were initially, and largely still are used as medications and chemical reagents, a practice which began in the late 19th century. In their use as medicine, nitrite vapors are often inhaled for relief of angina and other heart-related symptoms of disease. However when referred to as "poppers", alkyl nitrites representrecreational drugs.
Organic nitrites are prepared from alcohols and sodium nitrite in sulfuric acidsolution. They decompose slowly on standing, the decomposition products being oxides of nitrogen, water, the alcohol, and polymerization products of the aldehyde.
- In the laboratory, solutions of alkyl nitrites in glacial acetic acid are sometimes used as mild nitrating agents. The nitrating species formed is acetyl nitrate generated in situ.
- n-Butyl nitrite and ammonia convert phenylhydroxylamine to its nitrosamine derivative cupferron. Likewise pyrrolidine is a substrate for ethyl nitrite.
- Alkyl nitrites are also used in the formation of oximes with the stronger carbon acids and acid or base catalysis for example in the reaction of 2-butanone, ethyl nitrite and hydrochloric acid forming the oxime, the similar reaction with phenacyl chloride, or the reaction of phenylacetonitrile with methyl nitrite and sodium hydroxide.
An isolated but classic example of the use of alkyl nitrites can be found in Woodward's and Doering's quinine total synthesis:
for which they proposed this reaction mechanism:
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Answers:alkyl halides doesn't have any functional group. halide is not considered a functional group. if you look at organic chem book, halide is included in hydrocarbons because it doesn't really have any special function, probably except that the halides are good leaving group. they are really not interesting at all. but they are often used in substitution reactions since halides (except fluorides) are easily replaced. e.g. CH3Br + OH- ---> CH3OH CH3Br = methyl bromide or bromomethane CH3OH = methanol an example of functional group: ester (-COO-) is a functional group, it smells good. the good smell in fruit comes from ester.
Answers:Nitrate and iodide ion are nucleophiles. Benzyl chloride will react with nucleophiles by an Sn1 reaction. Bromobenzene undergoes electrophilic aromatic substitution. It won't react with nucleophiles.
Answers:The purpose of the NaHCO3 is to neutralize the excess HCl. CaCl2 is the drying agent. However, if you did not add enough CaCl2 to pick up all of the H2O, that would also distill into your product. I suspect that water is the contaminant in your distlllate. Add some more CaCl2 and swirl it until the CaCl2 has had a chance to pick up the excess water from your distillate. It is likely that you will lose some of the product but right now it appears that you have somewhat of a mess.
Answers:Leaving groups are extremely important, but don't forget that the more hindered your reactant is (for instance, triethylamine), the more partial it will be to an Sn1 reaction. A primary or methyl group would be much better for Sn2. Here are some other things to help you distinguish which type of reaction you're dealing with: Sn1: Tertiary reactants (because they form a more stable C+ ion) Have weak nucleophiles (Water, Any alcohol, etc.) Use polar protic solvents (Because Hydrogen bonds lower activation energy) The rate of the reaction is solely based on the concentration of your RX (alkyl halides) Sn2: Primary or methyl groups are best (steric hindrance can really mess up the ability for a concerted reaction) Strong nucleophiles help with abstracting hydrogens Polar aprotic solvents (No hydrogen bonding) Rate of the reaction can be increased from increasing the concentrations of the RX or the Nucleophile Hope this helps!