Advantages
i. Derivatives of alkylation are very stable ii. Some of these reactions can be done in aqueous solutions iii. Alkylation reagents are widely available iv. They are wither strong basic or acidic in nature.
Disadvantages
1. They are only limited to acid hydroxyl groups and amines
2. The reagents used are mostly toxic
Alkylating agents and how they act.
a. Boron trichloride in methanol or chloroethanol: an acidic hydrogen group undergoes esterification in the presence of boron trichloride an ester derivative. Acid BCl3
RCOOH + ClCH2CH2OH → RCOOCH2CH2Cl + H2O
b. Tetra-butyl-ammonium hydroxide (TBH): forms butyl ester with derivative or carboxylic acid that improves the retention time in the gas chromatography column. TBH
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Low volatile and non-volatile compounds can be easily made volatile
II. It is an easy method of derivatization
Disadvantages
I. Only aprotic organic solvents can be used.
II. Alcohol or water content is likely to affect the process of Silylation.
III. Carbowax columns are not compatible with silylating agents due to the presence of hydrogen in its stationary phase. Silylation reagents and their mechanisms Trimethylchlorosilane (TMCS),Hexamethyldisilazane (HMDS), Bistrimethylsilyltrifluoroacetamide (BSTFA), trimethylsilylimidazole (TMSI) among others. The listed reagents above react with acids and alcohol to give trimethylsilyl esters that give volatile and easily separable derivatives for Gas chromatography.
3) Acylation in Comparison to Silylation, this process targets the reduction in polarity of highly polar hydroxyl, amino, -thiol groups such as amino acids and carbohydrates by the addition of the addition of acyl group. It also makes it possible for compounds like sugar of high polarity to undergo Gas chromatography. Example of acylation is the reaction of alcohol and acetic anhydride to give acetic acid and acetate ester. CH3OCOCOCH3 + HOR → (in presence of H+ catalyst) CH3OCOR´ +
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Reagents are sensitive to moisture
III. They also have odor and can be hazardous
IV. Acidic by-product is formed by the reagents which can damage the columns during Gas chromatography Acylating reagents used and their mechanism of action;
Reagents used in acylation are mostly halogenated or contain halogen compounds in their structures.
I. Fluorinated anhydrides react with amines, phenols, and alcohols to give highly volatile and stable derivative of the prior analyte to be used. Acid receptor or amines are needed to enhance the reaction.
II. Penta-fluoro-benzoyl Chloride can be used for stoically hindered functional groups. It is can also be used in the derivatization of secondary amines which are highly sensitive and alcohols. An acid by-product e.g. hydrochloric acid is formed during the process but can be neutralized with the use of sodium hydroxide. Chiral derivatization in Gas Chromatography
Special reagents are required for the derivatization of chiral compounds which are superimposable and grouped as enantiomers. The reaction of purely chiral reagents with enantiomeric compounds will proceed to the formation of a racemic mixture that is two derivative enantiomers of one compound and is separated using gas Chromatography to give separate diastereomers for each enantiomer. Chiral derivatization is in high demand due to research on chiral
Because there are steric hindrance of two methyl groups on 4th carbon, the hydride is added to the endo side of the carbonyl group. 3. Reduction of Camphor produces a mixture of diastereomers. 4.
The reaction involves a nucleophilic acyl substitution on an aldehyde, with the leaving group concurrently attacking another aldehyde in the second step. First the Potassium hydroxide attacks a carbonyl, which forms a tetahedral intermediate which then collapses when attacked by another hydroxide. The carbonyl is formed again when its hydride attacks another carbonyl. In the final step of the reaction, the acid and alkoxide ions formed exchange a proton. In the presence of a very high concentration of base, the aldehyde first forms a doubly charged anion from which a hydride ion is transferred to the second molecule of aldehyde to form carboxylate and alkoxide ions. Subsequently, the alkoxide ion acquires a proton from the solvent.
Answer: Gas chromatography (GC) – utilized by scientists in order to be able to separate the volatile
Hydrogens, alkyls, or aryls bonded to carboxyl groups—made up of a carbonyl group and a hydroxyl group—are known as carboxylic acids. Derivatives of carboxylic acids include acid chlorides, esters, anhydrides, amides, and generally nitriles. These derivatives are formed by the replacement of the hydroxyl group with a different electronegative heteroatom substituent, which can be a single atom, such as a chlorine atom, or a group of atoms, such as in the formation of
Grignard reagents cannot be synthesized from alcohols because instead of reacting with the halide to form the Grignard reagent, the alcohol is deprotenated. Grignard reagents also cannot be synthesized from molecules with a carbonyl group.
1. We measured 2 mL of diluted hydrogen peroxide (the substrate), 1 mL of guaiacol (the product indicator), and 1 mL of neutral buffer (pH 7) with a syringe and disposed it into tubes 1, 2 , 4, 9, 11, and 12.
The product was placed in a Craig tube and several drops of hot (100°C) solvent (50% water, 50% methanol, by volume) was added and heated until all of the crystals dissolved. The Craig tube was plugged and set in an Erlenmeyer flask to cool. Crystallization was induced once the mixture was at room temperature by scratching the inner wall of the tube. It was then placed into an ice bath for ten minutes until crystallization was complete. The tube was then
To prepare and purify an ester: 1-pentyl ethanoate, using pent-1-ol and ethanoic acid. An annotated reaction showing this reaction is shown below:
In this experiment, 9-fluorenone was reduced with NaBH4 to produce 9-fluorenol and involves transfer hydrogenation. The hydride from NaBH4 was transferred to the electrophilic carbonyl carbon while the nucleophilic boron was attached to the carbonyl oxygen. If all four hydrogens from NaBH4 are transferred, then a borate salt is produced, which will decompose uon the addition of water. This will then produce
The products of interest within this experiment are 2-methyl-1-butene and 2-methyl-2-butene from sulfuric acid and phosphoric acid catalyzed dehydration of 2-methyl-2-butanol. The reaction mixture was then separated into its separate alkene components by steam distillation and then analyzed by gas chromatography (GC), Infrared Radiation (IR) spectroscopy, and Nuclear Magnetic Resonance (NMR) imaging. Gas chromatography is an analytical technique that is able to characterize if specific compounds exist in a reaction mixture, even if they are in low quantities, assess how much of a compound exists within a reaction mixture relative to other components within the sample, and determine the purity of an isolated product. In the case of this experiment, gas chromatography is used to analyze how pure the alkene reaction sample was and if any remnants of impurities or 2-methyl-2-butanol remained in the sample after isolation of alkene components.
The purpose of this lab was to synthesize the ester isopentyl acetate via an acid catalyzed esterification (Fischer Esterification) of acetic acid with isopentyl alcohol. Emil Fischer and Arthur Speier were the pioneers of this reaction referred to as Fischer Esterification. The reaction is characterized by the combining of an alcohol and an acid (with an acid catalyst) to yield and ester plus water. In order to accomplish the reaction, the reactants were
The synthesis of the alkyl halide n-Butyl Bromide from alcohol is the foundation for the experiment. During the isolation of the n-butyl bromide, the crude product is washed with sulfuric acid, water, and sodium bicarbonate to remove any remaining acid or n-butyl alcohol. The primary alkyl halide halide n-butyl bromide is prepared by allowing n-butyl alcohol to react with sodium bromide and sulfuric acid. The sodium bromide reacts with sulfuric acid to produce hydrobromic acid . Excess sulfuric acid acts to shift the equilibrium and speed up the reaction by producing a higher concentration of hydrobromic acid. The
A pre-weighed (0.315g) mixture of Carboxylic acid, a phenol, and neutral substance was placed into a reaction tube (tube 1). tert-Butyl methyl ether (2ml) was added to the tube and the solid mixture was dissolved. Next, 1 ml of saturated NaHCO3 solution was added to the tube and the contents were mixed separating the contents into three layers. Once this was completed
Most of the organic substances recovered from organic reactions are impure and require purification to obtain the desired pure product. The extracted benzoic
An alternative enzymatic method has been discovered to overcome the limitation of preparation of chitosan by discovering chitin deacetylases . For production of novel, well-defined chitosan we have found the use of chitin deacetylases for the conversion of chitin to chitosan, which is in contrast to the currently used chemical procedure, offers the possibility of a controlled, non-degradable process . This method is specially used to prepare chitosan oligomers