Chemistry Library

Nitrosoalkanes The nitrosoalkanes contain a nitroso-group, ーN=O, directly attached to a carbon atom. They are named as the nitroso-derivatives of the corresponding alkanes, e.g., (CH 3 ) 3 CNO                 2-methyl-2nitrosopropane General methods of preparation 1.  By the addition of nitrosyl chloride or bromide to alkenes, whereby alkene nitrosohalides are formed: CH 2 =CH 2    +    NOCl    ⟶     ClCH 2 CH 2 NO    (2 mol) ⟶    (ClCH 2 CH 2 NO) 2 2.  By the action of nitrous acid on certain types of compounds, e.g., secondary nitroalkanes. 3. By the oxidation of primary amines containing a tertiary alkyl group with e.g., Caro’s acid (peroxy-(mono) sulphuric acid): R 3 CNH 2    +    2[O]      (H 2 SO 4 ) ⟶     R 3 CNO   +   H 2 O On the other hand, Emmons (1957) has prepared primary, secondary and tertiary nitroso-compounds by oxidation of amines with neutralized peracetic acid in methylene dichloride (yield: 33-80 per cent). N-Substituted hydrox

Nitroalkane The nitroalkanes are colorless (when pure), pleasant-smelling liquids which are sparingly soluble in water. Most of them can be distilled at atmospheric pressure. Nomenclature The nitroalkanes are named as nitro-derivative of the corresponding alkane, the positions of the nitro-groups being indicated by numbers, e.g. CH 3 NO 2                                              nitromethane            NO 2     NO 2          |            | CH 3 CHCH 2 CHCH 2 CH 3                      2,4-dinitrohexane The nitroalkanes, the structure of which is RNO 2 , are isomeric with the alkyl nitrites, RONO. The evidence that may be adduced for these respective formulas is to be found in the study of the reactions of these two groups of compounds. It is, however, worthwhile at this stage to mention the reaction which most clearly indicates their respective structures, viz., reduction. When alkyl nitrites are reduced, an alcohol and ammonia or hydroxylamines are formed. Th

Cyanic acid Cyanic acid, HNCO. Urea, on dry distillation, gives cyanuric acid : 3CO(NH 2 ) 2     ⟶      H 3 N 3 C 3 O 3    +    3NH 3 Cyanuric acid is a colorless, crystalline solid, not very soluble in water, and is strongly acid, reacting as a mono-, di- and tribasic acid. It has a cyclic structure (a triazine derivative) and X-ray analysis indicates that the acid is best represented as a resonance hybrid. When cyanuric acid is heated, it does not melt but decomposes into cyanic acid vapour which, when condensed below 0 o C, gives a colorless condensate: H 3 N 3 C 3 O 3     ⟶      3HNCO Cyanic acid is a colorless, volatile, strongly acid liquid which above  0 o C , readily polymerises to cyanuric acid and cyamelide , (HNCO) n . Aqueus solutions of cyanic acid rapidly hydrolyse to give carbon dioxide and ammonia: HNCO    +    H 2 O      ⟶      CO 2    +    NH 3 There are two possible structures for cyanic acid, H-O-C = N and H-N=C=O. There is very lit

Cyanamide Cyanamide, m.p.42 o C, may be prepared by the action of ammonia on cyanogens chloride: ClCN    +    NH 3     ⟶      NH 2 CN    +    HCl It is also readily prepared by the action of water and carbon dioxide on calcium cyanamide. Cyanamide is converted into guanidine (q.v.) by ammonia and into thiourea (q.v.) by hydrogen sulphide. When cyanamide is melted it forms the dimer dicyandiamide , (NH 2 ) 2 C=NCN, and the trimer melamine, which is a cyclic compounds. X-ray analysis has shown that all the C-N bond lengths are the same. This can be explained on the assumption that melamine is a resonance hybrid of the amino-form ( cf. cyanuric acid). Melamine is manufactured by heating urea and passing the gaseous products over a heated catalyst: CO(NH 2 ) 2     (-NH 2 ) ⟶      HNCO     (6 mol)  ⟶     C 3 H 6 N 6    +    3CO 2 Melamine is used for making melamine-formaldehyde plastics. Cyanamide itself is a tautomeric compounds (amidine system), and Raman s

Cyanogens Cyanogen is also known as ethanedinitrile . Cyanogens may be prepared by heating the cyanides of mercury of silver. Hg(CN) 2     ⟶    (CN) 2    +   Hg Cyanogen is a poisonour, colourless gas, b.p. -21 o C, and is stable in spite of the fact that its heat of formation is +292.9 kJ mol -1 . It is hydrolysed by water, the main products being hydrocyanic acid and cyanic acid, and minor products being oxamide and ammonium formate. When cyanogens is heated at 400 o C, it polymerises to paracyanogen, which at 800 o C, regenerates cyanogens. The structure of cyanogens is probably best represented as a resonance hybrid, (I) being the most important:

Alkil isocyanides This is also known as isonitriles or carbylamines. General methods of preparation 1By heating an alkyl iodide with silver cyanide in aqueous ethanolic solution; a small amount of cyanide is also formed : RI    +    AgCN     ⟶      RNC    +    AgI 2   By heating a mixture of primary amine and chloroform with ethanolic potassium hydroxide:   RNH 2    +    CHCl 3    +    3KOH     ⟶      RNC    +    3KCl    +    3H 2 O 3 Dehydration of N-substituted formamides with phosphoryl chloride in pyridine produces isocyanides. RNHCHO      (POCl 3 )  ⟶     RNC General properties The alkyl isocyanides are poisonous, most unpleasant-smelling liquids, with lower boiling points than the isomeric cyanides. They are not very soluble in water, the nitrogen atom not having a lone pair of electrons available for hydrogen bonding. Alkyl isocyanides absorb in the region 2185-2120 cm -1 . Reaction 1.  Allkyl isocyanides are hydrolysed to an amine and form

Alkyl cyanide Alkyl cyanides are also known as nitriles or carbonitriles. Nomenclature This group of compounds is usually named either as the lakyl cyanides ( i.e ., the lakyl derivatives of hydrogen cyanide), or as the nitrile of the acid which is produced on hydrolysis, the suffix –ic of the trivial name being replaced by -onitrile , e.g . HCN                             hydrogen cyanide or formonitrile CH 3 CN                         methyl cyanide or acetonitrile (CH 3 ) 2 CHCN               isopropylcyanide or isobutyronitrile General methods of preparation 1. By the dehydration of acid amides with phosphorus pentoxide. High molecular weight acid amides are dehydrated to the corresponding cyanide by heat alone. Cyanides are prepared industrially by passing a mixture of carboxylic acid and ammonia over alumina at  500 o C . This reaction probably occurs as follows: RCO 2 H   +   NH 3     ⟶    RCO 2 NH 4    (Al 2 O 3 ) ⟶     H 2 O   +   RCONH 2    (Al 2

Ketens Ketens are compounds which are characterized by the presence of the grouping C=C=O. if the compounds is of the type RCH=C=O, it is known as an aldoketen; and if R 2 C=C=O, then a ketoketen. Ketoketens are generally prepared by debrominating an a-bromoacyl bromide with zinc, e.g., dimethylketen from a-bromoisobutyryl bromide: (CH 3 )CBrCOBr   +   Zn     ⟶     (CH 3 ) 2 C=C=O    +    ZnBr 2 Aldoketens are usually prepared by refluxing an acid chloride in pyridine solution, e.g ., CH 3 CH 2 COCl   +   C 5 H 5 N     ⟶      CH 3 CH=C=O    +    C 5 H 5 NH + Cl - The simplest member of the keten series is keten (ketene), CH 2 =C=O,   and may be prepared by debrominating bromoacetyl bromide with zinc: CH 2 BrCOBr   +    Zn     ⟶      CH 2 =C=O    +    ZnBr 2 It is, however, usually prepared by the thermal decomposition of acetone (ethyl acetate or acetic anhydride may also be used as the starting material): CH 3 COCH 3     ⟶     CH 2 =C=CO    +    C

Mesityl Oxide Mesityl oxide is a α,β-unsaturated ketone. The other name of mesityl oxide is 4-methylpent-3-en-2-one, b.p. 130 o C. This compound is a colorless,   volatile liquid with a honey-like odor. Mesityl oxide mey be prepared by distilling diacetone alcohol ( q.v .) with a trace of iodine: (CH 3 ) 2 C(OH)CH 2 COCH 3     (-H 2 O) ⟶     (CH 3 ) 2 C=CHCOCH 3    (90%) Stross et al . (1947) have shown that mesityl oxide prepared this way is a mixture of mesityl oxide and isomesityl oxide, CH 2 =C(CH 3 )CH 2 COCH 3 Mesityl oxide may also be prepared as follows: (CH 3 ) 2 C=CH 2  + CH 3 COCl   (ZnCl 2 )   ⟶  (CH 3 ) 2 CClCH 2 COCH 3    (-HCl)   ⟶   (CH 3 ) 2 C=CHCOCH 3 It is used as a solvent for oils, gums, etc.

Crotonaldehyde Crotonaldehyde ( but-2-en-1-al ), b.p. 104 o C, may be prepared by heating aldol alone, or better, with a dehydrating agent, e.g., zinc chloride. The best yield is obtained by distilling aldol with acetic acid as catalyst: CH 3 CHOHCH 2 CHO     (-H 2 O)   ⟶     CH 3 CH=CHCHO Crotonaldehyde closely resembles acraldehyde in its chemical properties. It exists, however, in two geometrical isomeric forms, cis and trans : A number of unsaturated aldehydes occur naturally in the essential oils, many accompanying the corresponding unsaturated alcohol. The simplest acetylenic aldehyde is propargylaldehyde (propiolaldehyde, propynal), b.p. 60 o C. This may be prepared from acraldehyde, the aldehyde group of which is ‘protected by acetal formation: It may also be obtained by the controlled oxidation of propargyl alcohol. Propargylaldehyde undergoes cleavage when treated with sodium hydroxide ( cf . acraldehyde, above):

 Methyl Vinyl Ether The simplest unsaturated ether is methyl vinyl ether, which is prepared industrially by passing acetylene into methanol at 160-200 o C in presence of 1-2 per cent potassium methoxide, and under pressure sufficient to prevent boiling: C 2 H 2    +   CH 3 OH      ⟶    CH 3 OCH=CH 2 The acetylene is diluted with nitrogen to prevent explosions. Methyl vinyl ether is a very reactive gas, b.p. 5-6 o C. It is hydrolysed rapidly by dilute acid at room temperature to give methanol and acetaldehyde ( cf . the ethers), but is stable in alkaline CH 3 OCH=CH 2    +    H 2 O      (H + )   ⟶     CH3OH    +    CH3CHO Solution. It undergoes many addition reactions at the double bond, e.g., CH 2 =CHOCH 3    +    HCl     (0 o C)   ⟶     CH 3 CHClーOーCH 3 CH 2 =CHOCH 3    +    CH 3 OH     (2.5 o c + trace of HCl)   ⟶    CH 3 CH(OCH 3 ) 2 It readily polymerises, and is used for making polyvinyl ether plastics.

Nitroglycerine Nitroglycerine is a poisonous, colorless, oily liquid, insoluble in water. It usually burns quietly when ignited, but when heated, rapidly struck or detonated, it explodes violently. Noble (1867) found that nitroglycerine could be stabilized by absorbing it in kieselguhr. This was dynamite, which is now, however, usually manufactured by using wood pulp as the absorbent, and adding solid ammonium nitrate. Blasting gelatin or gelignite is made by mixing nitroglycerine with gun-cotton (cellulose nitrate). The smokeless powder, cordite, is a mixture of nitroglycerine, gun-cotton and Vaseline. Nitroglycerine is also used in the treatment of angina pectoris. Nitroglycerine is manufactured by adding glycerol in a thin stream to a cold mixture of concentrated nitric and sulphuric acids: CH2OH                                   CH2ONO2 丨                                           丨 CHOH    +    3HNO3  ⟶      CHONO2  +   3H2O 丨