formaldehyde : properties Part 2

formaldehyde

source: testing lab

source: This land.illinois.edu

 formaldehyde : Chemical properties-

1) Condensation with phenol:

HCHO condenses with phenol to give a synthetic plastic bakelite. This reaction takes place in presence of dilute NaOH. Bakelite is used for preparing electrical insulators, electric switches, toys etc.

2) Condensation with urea :

HCHO also condenses with urea in acidic solution to form a plastic like product (formaldehyde urea plastic). It is used in the preparation of cup, plate, tray and glass etc.

3) Reaction with  alcohol:

HCHO reacts with CH₃OH in presence of dry HCl, then methylal (dimethoxy methane) is formed.

4) Addition reactions of Formaldehyde :

a) Addition of H₂—-

i) Aldehydes are reduced to primary alcohol.Reduction is carried out with LiAlH₄/ether, H₂/Pd,H₂/Ni etc.

>C=O +H₂ —->   >CHOH

HCHO + H₂——> CH₃OH (primary alcohol)

ii) Clemenson’s reduction-  When aldehydes are reduced with Zn-Hg/HCl then alkanes are formed.In this reaction >C=O is reduced to >CH₂ group.

>C=O +4[H] —->   >CH₂ +H₂O

HCHO +4[H]——–> CH4  + H₂O

b) Addition of HCN — Aldehydes on addition with  [NaCN & H₂SO_4] or HCN give cyanohydrins.

>C=O +HCN—–>    >C(OH) CN

HCHO + HCN—–>    HCH(OH) CN [formaldehyde cyanohydrin]

c) Addition of NaHSO₃— form crystalline Sodium bisulphite  compound.

>C=O + NaHSO₃ —–>    >C(OH) SO₃Na

HCHO + NaHSO₃—-> HCH(OH) SO₃Na [formaldehyde sodium bisulphite compd]

d) Addition of Grignard reagent– Form addition product  which on hydrolysis give primary alcohol.

>C=O +RMgX —–>   >C(OMgX) R——–>   >C(OH) R [sec.alcohol]

HCHO + CH₃MgBr —–>   HCH (OMgBr) CH₃——–>    CH₃CH₂OH [primary alcohol]

5) Substitution reaction of Formaldehyde-

a) Reaction with Hydroxylamine – Oximes are formed.

>C=O + H₂NOH——->       >C=NOH [oxime] +H₂O

HCH=O + H₂NOH——->       HCH=NOH [Formaldoxime]+H₂O

b) Reaction with Hydrazene –  Hydrazones are formed.

>C=O + H₂NNH₂——->       >C=NNH₂ [Hydrazone] +H₂O

HCH=O + H₂NNH₂——->       HCH=NNH₂[ formaldehyde hydrazone] +H₂O

c)  Reaction with Phenyl Hydrazene –  Phenyl Hydrazones are formed.

>C=O + H₂NNHC₆H₅ ——->       >C=NNHC₆H₅ [  Phenyl Hydrazone] +H₂O

HCH=O + H₂NNHC₆H₅——->  HCH=NNHC₆H₅ [Formaldehyde Phenyl  hydrazone] +H₂O

d)  Reaction with Semicarbazide –  Semicarbazones are formed.

>C=O + H₂NNHCONH₂——->       >C=NNHCONH₂ [  Semicarbazone] +H₂O

HCH=O + H₂NNHCONH₂  —–>  HCH=NNHCONH₂ [Formaldehyde Semicarbazone] +H₂O

e) Reaction with Phosphorous pentachloride—  Methylene dichloride is formed.

>C=O + PCl₅  ——>   >CCl₂ +POCl₃

HCH=O + PCl₅  ——>   CH₂Cl₂ [Methylene dichloride] +POCl₃

source: slide share.net