Substrates / reactants

Aniline
Formaline (formaldehyde solution)
Hydrochloric acid (HCl) as catalyst
Sodium hydroxide (NaOH) for neutralization
Water (in some experiments, extra water was added)

Reaction conditions

Condensation reaction: aniline + formaldehyde in the presence of HCl, at about 60–100 °C
Rearrangement reaction: acid-catalyzed conversion of O-ABA and P-ABA intermediates to MDA, at about 100–160 °C
Neutralization: with 49 wt% NaOH solution at higher temperature
Phase separation and washing with warm water
Reactor: 250 cm³ duplicated glass reactor with adjustable-speed stirrer; formaline dosing by a Metrohm Dozimat 765 programmable dosing unit
Operating parameters varied: aniline/formaldehyde ratio (A/F), HCl/aniline ratio (H/A), water/aniline ratio (W/A), condensation temperature (Tc), rearrangement temperature (Tr), condensation time (tc), rearrangement time (tr), formalin feed ratios (FR1, FR2), and formalin dosing time (tF)

Products

MDA isomers: 2,2′-MDA, 2,4′-MDA, and 4,4′-MDA
MDA oligomers / ring distribution: 2-ring, 3-ring, 4-ring, 5-ring, and ≥6-ring MDA content
By-products: mono-methyl MDA (MMM), N-methylated products, quinazolines
Intermediates: o-ABA and p-ABA (aminobenzylamine isomers), Animal (in the absence of acid)
Final downstream product: MDI (methylene diphenyl diisocyanate), formed by phosgenation of 4,4′-MDA