QUIMICA UNDECIMO SEMANA 23 FINAL

Main ideas & lessons (Carboxylic acids, importance, and reactions)

Chemistry “detectives” metaphor

• The class frames aroma/flavor detection in fruits as a chemical mystery.
• It emphasizes that organic compounds, especially carboxylic acids and their derivatives, can contribute to characteristic aromas (e.g., esters).

Core functional groups & key vocabulary

Carboxylic acids contain two main functional groups:

• Carbonyl (C=O)
• Hydroxyl (–OH)

The lesson highlights “5 key words” (related functional-group families):

• Carboxyl (carboxyl)
• Esters (esters)
• Alcohols (alcohols)
• Amides (amides)
• Nitriles (nitriles)

Physical & chemical properties of carboxylic acids

• Usually colorless liquids or crystalline solids, depending on molecular weight/structure.
• Tend to have higher boiling points than many hydrocarbons of similar mass.
• Solubility behavior
  • Lower carbon count → slightly more soluble in water
  • Longer carbon chain → solubility decreases
• Acid/base behavior
  • They are weak acids, donating protons in water to form carboxylate ions and hydronium.
  • They can react with bases to form carboxylate salts.
• Esterification (broad mention)
  • An overall transformation involving reaction between hydroxyl-containing groups and alcohols, producing water as part of the process.

---

Applications (why carboxylic acids matter)

• Ester synthesis
  • Food and fragrance industries (artificial flavors/aromas)
• Saponification
  • Alkaline hydrolysis of carboxylic acid esters to produce soaps
  • Links to fatty acids (long-chain carboxylic acids) reacting with strong bases
• Anhydrides synthesis
  • Via dehydration of two carboxylic acid molecules
  • Used in making esters, amides, and for polymer modification / chemical manufacturing
• Plastics & polymers
  • Used to produce polymers such as nylon and polyester
  • Carboxylic acids form “monomer” units that include the carboxyl group for stable polymer-building
• Pharmaceutical industry
  • Carboxylic acids as precursors for drugs such as anti-inflammatories, antibiotics, analgesics
• Coatings/formulations
  • Used for coating and as part of solution formulations

---

Main methods for obtaining (producing) carboxylic acids

(Methods to obtain carboxylic acids from other compounds.)

• Oxidation of alcohols
  • Oxidizing primary alcohols → yields carboxylic acids
• Oxidation of alkyl benzene
  • Oxidize an alkyl group attached to a benzene ring
  • The aromatic ring remains largely unchanged
  • Uses:
    • Potassium permanganate (KMnO₄)
    • Water and high temperature
• Hydrolysis of nitriles
  • Under acidic or basic medium, nitriles hydrolyze
  • Produces carboxylic acids
• Hydrolysis of acid derivatives (halide-related)
  • Water hydrolysis of acyl derivatives where “X” is a halogen (Cl, Br, I, F)
  • Produces:
    • Carboxylic acid
    • Byproduct: a halogen-derived acid (e.g., HCl / HBr / HI / HF)
• Carbonation of Grignard reagents (Greenar’s reagent)
  • Involves magnesium/halogen carbon chain and CO₂
  • Route variants:
    • More CO₂ / different conditions → carboxylic acid formation in basic medium
    • Another variant → carboxylic acid formation in acidic medium
• Malonic synthesis
  • A complex, multi-step route to a carboxylic acid
  • Core idea:
    • Uses a malonic (dibasic) precursor whose structure corresponds to an O=C–O pattern (part of the malonic structure, not “CO₂ itself”)
  • Outline (as described):
    • Use basic medium
    • Add a halogen-containing substituent to build the carbon skeleton
    • At high temperature in basic medium, eliminate one –COOH group
    • Net result: formation of a carboxylic acid with a substituted/branched side chain

---

Reactions of carboxylic acids (transformations derived from them)

1) Synthesis of acyl halides (“alkanoyl halides”)

• With phosphorus tribromide
  • Carboxylic acids + PBr₃ → bromoacyl halides
  • Example: ethanoic acid + PBr₃ → ethanoyl bromide
• With thionyl chloride
  • Carboxylic acids + SOCl₂ → chloroacyl halides
  • Example: ethanoic acid + SOCl₂ → ethanoyl chloride

2) Anhydride formation

• Carboxylic acids → anhydrides
• Mechanism concept:
  • Condensation of carboxylic acids with loss of water
  • Requires:
    • Considerable heating
    • Long reaction times
• Example:
  • Heating butanedioic acid (open chain) → forms butanedioic anhydride
  • Byproduct: water

3) Esterification

• Carboxylic acids + alcohols → esters
• Notes/conditions:
  • Mineral acid catalyst
  • Use excess alcohol to shift equilibrium toward ester formation (“mainly to the right”)
  • Water is harmful because it can hydrolyze the ester back, lowering yield
• Example:
  • Ethanoic acid + methanol (acid medium) → ester + water

4) Amide synthesis

• Carboxylic acids + ammonia or primary/secondary amines → amides
• Temperature note:
  • Requires certain temperatures, but lower than anhydride formation
• Example:
  • Ethanoic acid + ammonia → amide
• Byproduct:
  • Water (as described from the reacting acid components)

5) Reaction with organometallic reagents → ketone formation

• Carboxylic acids + organometallic compounds (two equivalents) + aqueous hydrolysis
  • Produces ketones
• Subtitle idea example:
  • Ethanoic acid + organometallic reagent → forms acetone

6) Reduction of carboxylic acids to alcohols

• LiAlH₄ (lithium aluminium hydride) reduces carboxylic acids → alcohols
• Conditions mentioned:
  • Ether medium (catalyst/solvent context)
  • Also mentions a basic medium in a later step
• Example:
  • Ethanoic acid → ethanol

7) Hell–Volhard–Zelinsky reaction (α-halo substitution)

• Purpose:
  • Add/position a halogen at the α-carbon (next to the carbonyl) of a carboxylic acid
• Reagent system:
  • Br₂ catalyzed by phosphorus
  • Phosphorus + bromine → PBr₃, which acts as the key catalyst
• Placement rule (as stated):
  • Halogen goes on the most substituted α-carbon possible (adjacent to the carbonyl carbon), subject to structural constraints

---

“Active break” (non-chemistry content)

Breathing and stretching

• Stand up, inhale/exhale, then stretch and rotate body.

Pictorial guessing game

• Screen shows Lego pieces and a black tile piece indicating a story.
• Correct answer identified: The Three Little Pigs
• Interpretation:
  • Pink Lego pieces = pig houses (walls/structures)
  • Black piece = the wolf trying to destroy the houses

---

Class wrap-up & exercise summary

• Students complete an activity: identify the reaction type for transformations involving carboxylic acid formation.
• Examples described:
  • Potassium permanganate involvement → indicates oxidation of alkenes
  • Presence of O₃ → indicates ozonolysis of alkenes/alkynes
  • Oxidation of primary alcohols and aldehydes → yields carboxylic acids (example references RCHO)
• Final reminders:
  • Review notes and finish the week’s activity
  • Support resources mentioned: tutoring, open classrooms, learning center spaces, and language courses

---

Speakers / sources featured

• No specific individual speakers are named in the subtitles.
• No explicit external sources/websites are credited.
• Background/transition music is referenced as “[Music]” (no artist credited).