Addition of hydroxylamine

A number of substances, such as the most commonly used sulfur dioxide, can reduce selenous acid solution to an elemental selenium precipitate. This precipitation separates the selenium from most elements and serves as a basis for gravimetry. In a solution containing both selenous and teUurous acids, the selenium may be quantitatively separated from the latter by performing the reduction in a solution which is 8 to 9.5 W with respect to hydrochloric acid. When selenic acid may also be present, the addition of hydroxylamine hydrochloride is recommended along with the sulfur dioxide. A simple method for the separation and deterrnination of selenium(IV) and molybdenum(VI) in mixtures, based on selective precipitation with potassium thiocarbonate, has been developed (69). 

Sulfamic acid can be made by many routes, including addition of hydroxylamine to SO2 and addition of NH3 to SO3 ... 

A somewhat unusual sequence to generate azepanones 80 involved the intramolecular addition of hydroxylamines to alkynes 76 to form cyclic nitrones 77. A vinyl magnesium bromide addition at low temperatures and a reduction with TiCls followed by N-Boc protection led to the azepane 78. Double bond bromination and subsequent RUO4 oxidation gave the lactam 79. Several further steps allowed the generation of the lactam structure 80 proposed for d,/-aca-cialactam, but the spectral data of the synthetic material differed from that of the natural product (Scheme 16)] [23 a, b]. 

The first reported synthesis of hydroxyurea (24) consists of the condensation of hy-droxylamine with potassium cyanate (Scheme 7.14) [87]. Condensation of hydroxy-lamine with ethyl carbamate also gives pure hydroxyurea in good yield after recrystallization (Scheme 7.14) [88]. Nitrogen-15 labeled hydroxyurea provides a useful tool for studying the NO-producing reactions of hydroxyurea and can be prepared by the condensation of N-15 labeled hydroxylamine with either potassium cyanate or trimethylsilyl isocyanate followed by silyl group removal (Scheme 7.14) [89, 90]. Addition of hydroxylamine to alkyl or aryl isocyanates yields alkyl or aryl N-hydroxyureas (Scheme 7.14) [91, 92]. The condensation of amines with aromatic N-hydroxy carbamates also produces N-substituted N-hydroxyureas (Scheme 7.14) [93]. 

The Beckmann rearrangement of oximes to produce amides is promoted by perrhenate ions under phase-transfer catalytic conditions, in the presence of trifluoro-methanesulphonic acid in nitromethane [6]. Under these conditions, the rearrangement reaction is frequently accompanied by the solvolysis of the oxime to the ketone. This can be obviated by the addition of hydroxylamine hydrochloride. No reaction occurs in the absence of the ammonium catalyst or with the O-acetyl oximes. 

Formally, they can all be viewed as derivatives of hydroxylamine, H2N—OH indeed, oximes can be prepared by the addition of hydroxylamine to aldehydes and ketones (equations 1 and 2), and hydroxamic acids by its reactions with acetyl halides and esters (equations 3 and 4). ... 

Intermolecular or intramolecular 1,4-addition of hydroxylamines as well as N- and 0-alkylhydroxylamines 39 to activated carbon-carbon double bonds (e.g. 40, equation 27) is widely used for preparation of both A-substituted, and A,A-disubstituted hydroxylamines. The addition proceeds regiospecifically. The most commonly utilized activating groups are ester , carboxyl , suRone , ketone and 2-pyridyl . Depending on reaction conditions, addition of hydroxylamines to a,/ -unsaturated ketones can be accompanied by formation of oximes . 

In most cases monoaddition products can be obtained in good yields , even in reactions with Michael acceptors possessing a terminal double bond . Further reaction with an excess of a Michael acceptor produces diaddition products in excellent yields . Sequential additions of hydroxylamine to endocyclic double bonds such as in 41 have also been applied for preparation of bridged heterocyclic systems of type 42 (equation 28) . 

Addition of hydroxylamines to an endocyclic bond is possible if the double bond is a part of an aromatic heterocyclic system (e.g. 43, equation 29) " ". ... 

Addition of hydroxylamines to Michael acceptors 44 possessing an ally lie leaving group results in formation of tandem addition-elimination products of type 45 (equation 30)". ... 

Addition of hydroxylamines as well as hydroxamates 48 to activated di- and trisubsti-tuted alkenes 49 (equation 32) results in the formation of one or two stereogenic centers at the a- and -positions of the product 50. 

Control of enantioselectivity in addition of hydroxylamines to prochiral activated double bonds has also been achieved through chiral catalysis. Substoichiometric amounts of magnesium bromide-chiral oxazoUdine complex 54 (equation 35) catalyze asymmetric addition of 0-benzylhydroxylamine to pyrazolides of a,/3-unsaturated acids 53 with moderate to good enantioselectivity ". 

Thermal addition of hydroxylamines to non-activated C=C bonds has been observed only during cyclization processes The reaction proceeds through a thermal retro-Cope mechanism as evidenced by its suprafacial stereospecihcity (equation 37). ... 

Intramolecular addition of hydroxylamines and hydroxamic acids to the non-activated double bonds is possible through oxidative cyclization. Reaction of O-Acyl fi,y-unsaturated hydroxamates (e.g. 56, equation 38) with bromine provides 3,4-substituted iV-hydroxy -lactams such as 57 with high diastereoselectivity. Analogous reaction of O-benzyl hydroxylamine 58 (equation 39) with iodine results in five-membered cyclization with 2 1 ratio of diastereomers. ... 

Addition of hydroxylamines to C=N double bonds produces stable compounds only for endocyclic C=N bonds. Addition of hydroxylamine to azirines of type 59 results in stable adducts 60 as seen in equation 40. Similar reactions have been observed in benzoxazoles and l,2,3-triazolo[4.5-rf]pyrimidones ° ... 

Tetramethyl-l,2-oxazepin-5-one and its N- methyl analogue have been prepared by the addition of hydroxylamine and N-methylhydroxylamine to phorone (73TL1615). 

Caution Since ( )-a-pinene is hydroborated to the dialkyl-borane state (R2BH), a large amount of hydrogen is evolved on addition of hydroxylamine-O-sulfonic acid. Consequently, the addition should be earned out dropwise and adequate ventilation should be provided. 

In many applications, relatively large quantities of anhydrous sodium sulfate can be added to the sample, prior to extraction by organic solvents, in order to enhance the partitioning process (333-336, 341, 342, 354, 365, 370). In some instances, such as in the analysis of clorsulon in bovine liver and milk, addition of hydroxylamine hydrochloride is often recommended prior to extraction (329, 360). The use of this agent is to prevent interactions between the analyte and endogenous aldehydes that lead to loss of recovery. 

In the course of redox pyrrolization of the oxime 39 with X = OH, the hydroxyl group in position 5 is vinylated to a slight extent to form 1-vinyl-5-vinyloxy-4,4,6,6-tetramethyl-4,5,6,7-tetrahydro-5-azaindole (40, X = OCH=CH2). This was the first example of nucleophilic addition of hydroxylamine to a triple bond not activated by strong electron-withdrawing substituents. x... 

Thus, the direction of addition of hydroxylamine derivatives to acetylenes is affected by not only steric, but also by electronic factors as well. 

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