Chemca
Master Organic Conversions
The 2-Step Playbook
Unlock the logic of organic synthesis. This curated list features 20 critical two-step conversions spanning all Class 11 and 12 organic chapters (Haloalkanes, Alcohols, Aldehydes, Amines). Click on any conversion to reveal a highly descriptive, mechanistic breakdown along with flawlessly formatted chemical equations.
1 Convert Ethanol to But-1-yne
To increase the carbon chain, we first need to convert the unreactive alcohol into a reactive alkyl halide. Ethanol is treated with Thionyl chloride ($\ce{SOCl2}$) in the presence of pyridine. This is the preferred method because the byproducts ($\ce{SO2}$ and $\ce{HCl}$) are gases that escape, leaving pure Chloroethane.
The carbon chain must be extended from 2 to 4 carbons while introducing a triple bond. Chloroethane is reacted with Sodium acetylide ($\ce{NaC\equiv CH}$). The acetylide ion acts as a strong nucleophile, executing an $S_N2$ attack on the ethyl chloride, resulting in the terminal alkyne But-1-yne.
2 Convert Benzene to Aniline
Benzene cannot be directly converted to an amine. First, it undergoes nitration. Benzene is heated with a nitrating mixture (concentrated Nitric acid and concentrated Sulfuric acid at 323-333 K). The $\ce{H2SO4}$ acts as an acid to generate the powerful nitronium electrophile ($\ce{NO2+}$), yielding Nitrobenzene.
Nitrobenzene is then subjected to reduction. The most common and industrially preferred laboratory method is treating it with active metal and acid, specifically Tin and Hydrochloric acid ($\ce{Sn/HCl}$). This reduces the $-\ce{NO2}$ group to an $-\ce{NH2}$ group, producing Aniline.
3 Convert Toluene to Benzaldehyde
To selectively oxidize the methyl group without over-oxidizing it to benzoic acid, we use halogenation. Toluene is treated with Chlorine gas ($\ce{Cl2}$) in the presence of boiling temperature or UV light ($h\nu$). This triggers a free-radical substitution on the side chain, specifically substituting two hydrogen atoms to form Benzal chloride ($\ce{C6H5CHCl2}$).
The gem-dihalide (benzal chloride) is then subjected to hydrolysis by heating with water (or aqueous alkali) at 373 K. The two chlorine atoms are replaced by two $-\ce{OH}$ groups forming an unstable gem-diol. This intermediate immediately loses a water molecule to form the stable carbonyl group of Benzaldehyde.
4 Convert Propene to Propan-1-ol
Direct hydration of propene yields propan-2-ol (Markovnikov). To get the primary alcohol, we must first add a halogen to the terminal carbon. Propene is treated with Hydrogen Bromide ($\ce{HBr}$) in the presence of an organic peroxide (Kharasch effect). This free-radical addition strictly follows Anti-Markovnikov's rule, yielding 1-Bromopropane.
The primary alkyl bromide is now converted to an alcohol. 1-Bromopropane is boiled with aqueous Potassium Hydroxide ($\ce{KOH (aq)}$). The nucleophilic hydroxide ion ($OH^-$) substitutes the bromide ion via an $S_N2$ mechanism, successfully forming Propan-1-ol.
5 Convert Ethanoic acid to Methanamine
We need to step down the carbon series (from 2 carbons to 1 carbon). The prerequisite for a step-down reaction is an amide. Ethanoic acid (Acetic acid) is treated with Ammonia ($\ce{NH3}$) to form ammonium ethanoate, which upon strong heating loses water to form Ethanamide (Acetamide).
Ethanamide is subjected to the Hoffmann bromamide degradation by reacting it with Bromine ($\ce{Br2}$) and strong aqueous or alcoholic alkali ($\ce{KOH}$/$\ce{NaOH}$). The carbonyl carbon is completely eliminated as potassium carbonate, leaving a primary amine with one less carbon atom: Methanamine (Methylamine).
6 Convert Phenol to Salicylic acid
To activate the benzene ring for a weak electrophile ($\ce{CO2}$), phenol must be converted to the highly reactive phenoxide ion. Phenol is treated with aqueous Sodium Hydroxide ($\ce{NaOH}$) to yield Sodium phenoxide. The phenoxide ion is significantly more reactive towards electrophilic aromatic substitution than phenol itself.
Sodium phenoxide is heated with Carbon dioxide ($\ce{CO2}$) at 400 K under a pressure of 4-7 atmospheres. The electrophilic carbon attacks the ortho position. Subsequent acidification ($\ce{H+}$ or dilute $\ce{HCl}$) of the resulting salt yields 2-Hydroxybenzoic acid, commonly known as Salicylic acid.
7 Convert Ethene to Ethanoic acid
The double bond of ethene must be converted to a functional group capable of oxidation. Ethene gas is passed through water in the presence of a few drops of concentrated Sulfuric acid (acid-catalyzed hydration). The electrophilic addition of water across the double bond yields Ethanol.
Ethanol (a primary alcohol) is subjected to vigorous oxidation using alkaline Potassium Permanganate ($\ce{KMnO4 / KOH}$) followed by acid hydrolysis ($\ce{H3O+}$), or directly with acidified Potassium Dichromate ($\ce{K2Cr2O7 / H2SO4}$). The primary alcohol bypasses the aldehyde stage and is oxidized directly to Ethanoic acid (Acetic acid).
8 Convert Bromomethane to Propanone
To build a ketone from a 1-carbon halide, we need to add 2 carbons. First, add one carbon via nucleophilic substitution. Bromomethane ($\ce{CH3Br}$) is reacted with alcoholic Potassium Cyanide ($\ce{KCN}$). The nucleophilic cyanide ion attacks the methyl carbon, forming Ethanenitrile (Acetonitrile) and increasing the chain length to 2.
Ethanenitrile is treated with Methylmagnesium bromide ($\ce{CH3MgBr}$, a Grignard reagent) in dry ether. The nucleophilic methyl carbanion attacks the electrophilic nitrile carbon, forming an imine salt intermediate. Subsequent acid hydrolysis ($\ce{H3O+}$) cleaves the imine to yield Propanone (Acetone) and ammonia gas.
9 Convert Aniline to Chlorobenzene
Aniline cannot be directly chlorinated to yield exclusively chlorobenzene. It must be converted into a highly reactive intermediate. Aniline is treated with a cold mixture (273-278 K) of Sodium Nitrite and Hydrochloric acid ($\ce{NaNO2 + HCl}$/HONO). This converts the primary amine into Benzene diazonium chloride.
The exceptionally good leaving group (nitrogen gas, $\ce{N2}$) allows for easy nucleophilic aromatic substitution. The freshly prepared diazonium salt is treated with Cuprous Chloride dissolved in Hydrochloric acid ($\ce{Cu2Cl2 / HCl}$). This replaces the diazonium group with a chlorine atom, yielding Chlorobenzene.
10 Convert Propan-1-ol to Propan-2-ol
To shift the position of the hydroxyl group from a primary to a secondary carbon, we must first form a double bond. Propan-1-ol is heated with concentrated Sulfuric acid ($\ce{H2SO4}$) at 443 K. This dehydrates the alcohol via $\beta$-elimination to form an alkene, Propene.
The alkene is now re-hydrated. Passing propene through water in the presence of dilute acid ($\ce{H2O/H+}$) leads to electrophilic addition. According to Markovnikov's rule, the negative part of the addend (the $\ce{OH-}$ group) attaches to the carbon with fewer hydrogen atoms (the secondary carbon). This yields Propan-2-ol.
11 Convert Chlorobenzene to p-Nitrophenol
Chlorobenzene is treated with a nitrating mixture (conc. $\ce{HNO3}$ and conc. $\ce{H2SO4}$). The chlorine atom is an ortho/para-directing group due to resonance. This yields a mixture of o-nitrochlorobenzene and p-nitrochlorobenzene (the major product, due to less steric hindrance), which is separated.
Usually, haloarenes are unreactive towards nucleophilic substitution. However, the presence of the strongly electron-withdrawing nitro group ($\ce{-NO2}$) at the para position drastically increases the reactivity. Heating p-nitrochlorobenzene with 15% aqueous $\ce{NaOH}$ at a moderate 433 K, followed by acidification ($\ce{H+}$), replaces the chlorine with a hydroxyl group, yielding p-Nitrophenol.
12 Convert Benzyl chloride to 2-Phenylethanoic acid
To synthesize an acid with one additional carbon atom compared to the starting material, cyanide substitution is ideal. Benzyl chloride ($\ce{C6H5CH2Cl}$) is boiled with alcoholic Potassium Cyanide ($\ce{KCN}$). The cyanide nucleophile replaces the chloride ion via $S_N2$ mechanism, resulting in Benzyl cyanide (Phenylethanenitrile, $\ce{C6H5CH2CN}$).
The nitrile group ($\ce{-C\equiv N}$) is highly susceptible to hydrolysis. Boiling benzyl cyanide with dilute mineral acid (represented as $\ce{H3O+}$ or $\ce{H2O/H+}$) completely hydrolyzes the carbon-nitrogen triple bond, converting it directly into a carboxylic acid group, producing 2-Phenylethanoic acid.
13 Convert Ethanal to But-2-enal
Ethanal (acetaldehyde) contains $\alpha$-hydrogen atoms. Treatment with dilute alkali (like 10% $\ce{NaOH}$) triggers an Aldol addition. An enolate ion generated from one molecule attacks the carbonyl carbon of another. The resulting product is a $\beta$-hydroxyaldehyde: 3-Hydroxybutanal (aldol).
Aldols are relatively unstable to heat because elimination of water leads to a highly stable, conjugated system. Heating 3-Hydroxybutanal causes an E1cB elimination of a water molecule from the $\alpha$ and $\beta$ positions, yielding the $\alpha,\beta$-unsaturated aldehyde, But-2-enal (Crotonaldehyde).
14 Convert But-1-ene to But-2-ene
To move the double bond inward, we first add a halogen to the secondary carbon. But-1-ene is reacted with Hydrogen Bromide ($\ce{HBr}$) in the dark/absence of peroxides. The electrophilic addition follows Markovnikov's rule, placing the bromine atom on the more substituted carbon, yielding 2-Bromobutane.
The secondary alkyl halide is then subjected to dehydrohalogenation by heating with alcoholic Potassium Hydroxide ($\ce{KOH(alc)}$). The $\beta$-elimination strictly follows Saytzeff's rule, which dictates that the major product will be the highly substituted, thermodynamically stable alkene. Thus, the double bond forms internally, yielding But-2-ene.
15 Convert Benzene to Phenol
Direct hydroxylation of benzene is not possible. Benzene is first subjected to electrophilic aromatic substitution by heating it with Oleum (fuming sulfuric acid, $\ce{H2S2O7}$). The active electrophile ($\ce{SO3}$) attacks the ring to form Benzene sulfonic acid.
The sulfonic acid group is converted to a hydroxyl group via the industrial fusion method. Benzene sulfonic acid is fused with solid Sodium Hydroxide ($\ce{NaOH}$) at high temperatures (573-623 K) to form sodium phenoxide, followed immediately by acidification ($\ce{H+}$) to liberate pure Phenol.
16 Convert Methyl bromide to Acetic acid
Methyl bromide (1 carbon) must be stepped up to a 2-carbon compound. It is heated with an alcoholic solution of Potassium Cyanide ($\ce{KCN}$). The cyanide ion is an ambident nucleophile, but carbon-carbon bond formation is favored. This $S_N2$ reaction yields Acetonitrile (Ethanenitrile).
The nitrile group is converted into a carboxylic acid through hydrolysis. Boiling acetonitrile with dilute aqueous acid (e.g., dilute $\ce{H2SO4}$ or $\ce{HCl}$, represented as $\ce{H3O+}$) completely breaks the triple bond, substituting it with oxygen and a hydroxyl group, thus yielding Acetic acid (Ethanoic acid).
17 Convert Ethanol to Propanenitrile
Hydroxyl groups are poor leaving groups, making direct substitution by cyanide impossible. Ethanol is first reacted with Phosphorus Pentachloride ($\ce{PCl5}$) or Thionyl Chloride ($\ce{SOCl2}$) to replace the $-\ce{OH}$ group with a much better leaving group, a chlorine atom. This yields Chloroethane.
Chloroethane (2 carbons) is then treated with alcoholic Potassium Cyanide ($\ce{KCN}$). The nucleophilic attack of the cyanide ion displaces the chloride ion, simultaneously adding a third carbon atom to the chain. The resulting product is Propanenitrile (Ethyl cyanide).
18 Convert Benzene to 1-Phenylethanol
An alkyl group with an oxygen attached must be introduced to the ring. Benzene is treated with Acetyl chloride ($\ce{CH3COCl}$) in the presence of anhydrous Aluminum chloride ($\ce{AlCl3}$). The Lewis acid generates the acylium ion electrophile ($\ce{CH3CO+}$), yielding the ketone Acetophenone.
The carbonyl group of acetophenone is then reduced to a secondary alcohol. This is selectively achieved using Sodium Borohydride ($\ce{NaBH4}$) in ethanol, or Lithium Aluminum Hydride ($\ce{LiAlH4}$). The nucleophilic hydride attack yields 1-Phenylethanol.
19 Convert Aniline to Fluorobenzene
Direct fluorination of benzene rings is explosive and impossible to control. The amino group provides the pathway. Aniline is reacted with Sodium Nitrite and Hydrochloric acid at 273 K ($\ce{NaNO2 / HCl}$) to form the indispensable Benzene diazonium chloride salt.
The diazonium chloride is treated with Fluoroboric acid ($\ce{HBF4}$) to form an insoluble precipitate of benzene diazonium fluoroborate ($\ce{C6H5N2+BF4-}$). Upon careful heating ($\Delta$), this salt decomposes, expelling nitrogen gas and boron trifluoride, leaving behind pure Fluorobenzene.
20 Convert Propene to Propyne
To create a triple bond, two molecules of hydrogen halide must be eliminated. First, we need two halogens. Propene is reacted with Bromine in a non-polar solvent like Carbon Tetrachloride ($\ce{Br2/CCl4}$). This anti-addition across the double bond yields the vicinal dihalide, 1,2-Dibromopropane.
The vicinal dihalide undergoes two successive elimination reactions. While alcoholic KOH can perform the first elimination, a much stronger base is required to eliminate the second $\ce{HBr}$ molecule from the resulting vinyl bromide. Therefore, heating with strong Sodium amide ($\ce{NaNH2}$ in liquid $\ce{NH3}$) executes a complete double elimination to yield Propyne.
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