In decarboxylation of sodium salts of carboxylic acids, CaO (calcium oxide) is used along with soda lime.

What is Soda Lime?

Soda lime = NaOH + CaO

CaO itself does not take part directly in the reaction but plays an important supporting role.

Reaction

Role of CaO

1. Acts as a catalyst.
2. Keeps the mixture dry (dehydrating agent).
3. Prevents fusion (lumping) of NaOH during heating.
4. Provides porous surface for smooth reaction.

It does not get consumed in the reaction.

Decarboxylation proceeds via formation of a carbanion intermediate.

Therefore:

• More stable carbanion → easier decarboxylation
• Electron-withdrawing groups increase rate

Decarboxylation is easier when the resulting carbanion is stable:

$$\text{CH}_3COONa > \text{C}_2H_5COONa$$

Methyl carbanion is slightly more stable than higher alkyl due to less +I effect.

Only sodium salts undergo smooth decarboxylation.
Free acids do not give the same clean reaction under these conditions.

f soda lime is absent and only NaOH is used:

Reaction still occurs, but less efficient due to fusion of NaOH

The Sabatier–Senderens reaction is a catalytic hydrogenation reaction in which unsaturated compounds (alkenes or alkynes) are reduced to saturated compounds (alkanes) using hydrogen gas (H₂) in the presence of a metal catalyst such as Ni, Pt, or Pd.

It is named after the French chemists

• Paul Sabatier
• Jean-Baptiste Senderens

Paul Sabatier received the 1912 Nobel Prize in Chemistry for his work on catalytic hydrogenation.

What JEE / NEET Can Ask

Concept-Based Questions

• Type of catalysis → Heterogeneous catalysis
• Catalyst used → Ni (most common), Pt, Pd
• Nature of reaction → Addition (Reduction) reaction
• Mechanism → Adsorption theory

Mechanism (Very Important for JEE)

✔ Hydrogen adsorbs on Ni surface
✔ H–H bond breaks → Atomic hydrogen formed
✔ Alkene/Alkyne adsorbs
✔ Syn addition of hydrogen
✔ Alkane formed

🔥 Very Important Concept

✔ Syn addition may give cis product
✔ But syn ≠ cis always

Example:

Hydrogenation of cycloalkene → gives cis product
But hydrogenation of 2-butene → gives alkane (no cis/trans left)

So in that case:
Syn addition happened
But cis concept disappears

Syn Addition (Mechanism term)

• Refers to how groups are added during a reaction.
• Both substituents add from the same face of the double bond.
• It is a mechanistic term.

Example:
Hydrogenation using H₂/Ni (Sabatier–Senderens) → Syn addition

What is Syn Addition?

The addition of two substituents to the same side (or face) of a double or triple bond reduces the bond order but increases the number of substituents.

Raney nickel is significantly more reactive than standard nickel powder.  It is Created from a 

$$ Nickel-Aluminum alloy, where Aluminum is removed by caustic leaching (NaOH)

Platinum (like Ni, Pd) mainly prefers:$$\boxed{C=C > C\equiv C > C=O \gg Aromatic\ ring}$$

In a benzylidene compound containing a ketonic (C=O) group, when is only the C=C reduced?

Consider a Typical Example

Benzylidene acetone type compound:

$$Ph-CH=CH-CO-CH_3$$Ph−CH=CH−CO−CH3​

This contains:

• Aromatic ring
• C=C (alkene)
• C=O (ketone)
• Conjugation

Only Double Bond is Reduced When:

Mild catalytic hydrogenation conditions are used:

$$\boxed{H_2 / Pd \text{ or } Pt \text{ (room temp, low pressure)}}$$H₂​/Pd or Pt (room temp, low pressure)​

Under these conditions:$$Ph-CH=CH-CO-CH_3 \quad \xrightarrow{H_2/Pd} \quad Ph-CH_2-CH_2-CO-CH_3$$

✔ C=C reduced
✔ C=O remains intact
✔ Benzene untouched

Why C=C Reduces First?

Reactivity order:

$$C=C > C=O \gg Aromatic\ ring$$

Reasons:

1. Alkene π bond adsorbs more easily on metal surface
2. C=O is stabilized by resonance
3. Conjugation increases stability of carbonyl

When Will C=O Also Reduce?

If you use:

• High pressure
• High temperature
• Excess hydrogen
• More active catalyst

Then both C=C and C=O may reduce.

Important JEE Rule (Remember This)

In α,β-unsaturated ketones (benzylidene type compounds):

Catalytic hydrogenation (mild) → 1,4-reduction (C=C reduction)
Strong hydride reagents (NaBH₄) → 1,2-reduction (C=O reduction)

Can NaBH₄ reduce a double bond (C=C)?

Short Answer:

$$\boxed{\text{No, NaBH}_4 \text{ does NOT reduce C=C}}$$​

What NaBH₄ Actually Reduces

NaBH₄ is a mild hydride donor.

It reduces:

✔ Aldehydes (–CHO) → 1° alcohol
✔ Ketones (>C=O) → 2° alcohol

Practical Reactivity Comparison of Common Reducing Agents (JEE Main + Advanced level)

NaBH₄ (Sodium borohydride)

✔ Reduces:

• Aldehydes → 1° alcohol
• Ketones → 2° alcohol

❌ Does NOT reduce:

• C=C
• C≡C
• Carboxylic acids
• Esters
• Amides
• Benzene ring

📌 Mild, selective carbonyl reducer
📌 Works in alcohol solvent

LiAlH₄ (Lithium aluminium hydride)

✔ Reduces:

• Aldehydes
• Ketones
• Esters → 1° alcohol
• Carboxylic acids → 1° alcohol
• Amides → amines
• Acid chlorides

❌ Does NOT reduce:

• C=C
• Benzene ring

📌 Very strong hydride donor
📌 Requires dry ether

H₂ / Ni, Pd, Pt (Catalytic hydrogenation)

✔ Reduces:

• C=C
• C≡C
• Aldehydes (under suitable conditions)
• Ketones (under stronger conditions)

❌ Usually does NOT reduce:

• Esters (mild conditions)
• Benzene ring (needs high pressure)

📌 Works by surface adsorption
📌 Prefers C=C over C=O

Lindlar Catalyst

✔ Reduces:

• Alkyne → cis-alkene only

❌ Does NOT reduce:

• Further to alkane
• Carbonyl

📌 Very selective

Na / NH₃ (Dissolving metal reduction)

✔ Reduces:

• Alkyne → trans-alkene

NOTE : Reduction is highly stereoselective , giving predominantly cis -isomer

NOTE : Pd isomerises the alkene hence with Pd , trans -isomer predominates.

Palladium can catalyze alkene isomerisation via reversible adsorption on its surface, leading to thermodynamic control where the more stable trans isomer predominates.

Note: When Cyclopropane/butane reacts with hydrogen gas in the presence of Ni, it gives propane/butane

he ring opens due to high strain and behave like an alkene

Cyclobutane also has ring strain (90° vs 109.5°)

Less than cyclopropane but still significant

Ring opens under catalytic conditions

Important JEE/NEET Concept

Reactivity order due to ring strain:
Cyclopropane> Cyclobutane > Cyclopentane

Cyclopentane and cyclohexane usually do NOT open easily.

When 100 mL of water is mixed with 400 mL of ethanol, the total volume is not simply additive — because hydrogen bonding causes volume contraction.

Reason:

Water and ethanol molecules form strong hydrogen bonds, allowing the molecules to pack more closely.
So the mixture’s final volume is less than 500 mL.

Experimental result:

When equal amounts of water and ethanol are mixed, the volume contraction is about 4–5%.

The maximum number of carbon atoms found in naturally occurring monosaccharides is nine (9).

Explanation:

Monosaccharides are classified by the number of carbon atoms:

A native protein is a protein in its natural, functional, and properly folded form (the form found in living cells).

Structure of native protein

A native protein usually has its secondary, tertiary, and sometimes quaternary structure intact.

That’s what gives it its specific shape and biological activity.

Summary

Secondary Structure Proteins

• Meaning: Local folding of polypeptide chains into α-helix or β-pleated sheets (held by hydrogen bonds).
• Examples:
  • Keratin → mostly α-helix (found in hair, nails, wool).
  • Fibroin → mostly β-pleated sheet (found in silk).

Tertiary Structure Proteins

• Meaning: 3D folding of a single polypeptide chain → forms a globular protein.
• Forces involved: H-bonds, disulfide bridges, ionic bonds, hydrophobic interactions.
• Examples:
  • Myoglobin → stores oxygen in muscles.
  • Lysozyme → enzyme that breaks bacterial cell walls.
  • Ribonuclease → enzyme for RNA breakdown.

Quaternary Structure Proteins

• Meaning: Association of two or more polypeptide chains (subunits) in a functional complex.
• Examples:
  • Hemoglobin → 4 subunits (2 α + 2 β chains).
  • Insulin → made of multiple polypeptide chains (A and B chains linked by disulfide bonds).
  • DNA polymerase → multi-subunit enzyme.

Fructose is a reducing sugar, even though it’s a ketose (contains a keto group), not an aldehyde.
Let’s see how?

1. Reducing sugar meaning

A reducing sugar is one that can reduce mild oxidizing agents like Tollens’ reagent (Ag⁺ → Ag) or Fehling’s solution (Cu²⁺ → Cu⁺) — because it has a free aldehyde or ketone group (or can form one in solution).

2. Fructose has a ketone group (not aldehyde)

At first glance, this looks non-reducing because it lacks a free aldehyde group.

3. In alkaline medium → tautomerization

In basic solution, fructose undergoes keto–enol tautomerism, forming an enediol intermediate.
This intermediate can rearrange to give glucose and mannose, both of which are aldehydes (aldoses). Fructose⇌enediol formalkaline mediumGlucose+Mannose\text{Fructose} \xrightleftharpoons[\text{enediol form}]{\text{alkaline medium}} \text{Glucose} + \text{Mannose}Fructosealkaline mediumenediol form​Glucose+Mannose

4. Hence → Reducing property

Because glucose and mannose can reduce Tollens’ and Fehling’s reagents, fructose also gives a positive test indirectly.
So, fructose is a reducing sugar — not directly, but via tautomeric conversion to an aldehyde sugar.

Urotropin is another name for hexamethylenetetramine (chemical formula: C₆H₁₂N₄).

🔹 Chemical Information

• IUPAC Name: Hexamethylenetetramine
• Molecular Formula: C₆H₁₂N₄
• Molar Mass: 140.19 g/mol
• Structure: It is a cage-like compound made up of four nitrogen atoms linked by methylene (-CH₂-) groups.

🔹 Preparation

Urotropin is formed by the reaction of formaldehyde with ammonia.

6HCHO + 4NH₃→ C₆H₁₂N₄ + 6H₂O

🔹 Uses

1. Medicine: Used in the treatment of urinary tract infections (UTIs) because in acidic urine, it releases formaldehyde, which acts as an antiseptic.
2. Explosives: Used in the preparation of RDX (Cyclonite), a powerful explosive.
3. Fuel tablets: Used in solid fuel tablets for camping and military use (burns smokelessly).
4. Plastics & resins: Used in making phenol-formaldehyde resins.