Selenosemicarbazides

The ability of various selenium heterocycles to check the loss of orthophosphate caused by irradiation of ATP has been studied by Brucker and Bulka (92). They found that only 2-amino-4,5-dimethyiselenazole shows radioprotective properties, while other 2-aminoselenazoles, selenosemicarbazides, and acetone selenosemicar-bazones possess no such activity but are in addition very sensitive to radiation (93). 

The selenosemicarbazides 165 were cyclized to yield the corresponding 3-alkylsclcno-l //-l, 2,4-triazoles 166a-g (Equation 52 and Table 34) <2006H(68)1191>. 

Table 34 Cyclization of selenosemicarbazides to give 3-alkylseleno-1H-1,2,4-triazole derivatives (Equation 52)...

Selenosemicarbazide (H2NN(H)C(Se)NH2) was used by Velykanov et al. to make Cd, Zn, Ag, and Hg selenide films and precipitates from aqueous alkaline solutions [12]. As with the other Se precursors, Na2S03 was used to stabilize the selenosemicarbazide against rapid decomposition. This reagent was reputed to be more stable than the previous two. 

One example is given in the literatnre where selenosemicarbazide was nsed to deposit CdSe from solutions containing different complexants [99]. This reagent was apparently more stable than selenonrea or A,A-dimethylselenonrea, and it is snrprising that it does not appear to have been snbseqnently nsed. The CdSe films were specular and had a resistivity of 10 -10 O-cm, which dropped abont an order of magnitude on illumination. 

Selenosemicarbazide was used in one study to make, among other materials, ZnSe films and precipitates from aqueous ammoniacal solutions at 20°C [99]. The films were specular, but no further information was provided. 

Ag2Se films were first deposited from a bath nsing selenosemicarbazide as a Se source and thiourea to complex the Ag at 20°C [93], The films were specular and had a resistivity of between 2 and 20 H-cm. 

Diacetyl monoxime + semicarbazide, thiosemicarbazide or selenosemicarbazide [Cr(LH)L] [Cr(LH)(H20)3lCl2 (semicarbazone only) 20... 

The complexes of selenocysteamine of type 505 [897], selenosemicarbazide 506 [898], selenosemicarbazones 507 [899], benzoselenazoles [900], and 2-(2-pyridine)benzose-lenophene 508 [901] have been comprehensively examined in a monograph [1, vol.2] ... 

Selenadiazoline (172) and similarly very crowded derivatives are prepared as outlined in Scheme 78 (76JCS(P1)2079). Cyclic condensation of selenosemicarbazide and carboxylic acids affords the 2-acylamino derivative (184) and, by hydrolysis, 2-amino-l,3,4-selenadiazoles (185 Scheme 79) (71JHC835, 73JPS839). 

Another variation of this synthesis involves cyclization of 4-substituted 1-acyl-selenosemicarbazides (Scheme 80) (73JPR164). 2,5-Diamino-l,3,4-selenadiazoles of type (187) are prepared from bis(selenourea) (186 Scheme 81) (73JPR155). 

Treatment of thiohydrazides with nitrous acid leads to formation of thiatriazoles. 5-Amino-l,2,3,4-selenatriazoles may be prepared in the same manner from the corresponding selenosemicarbazides (83 R1 = R -Et, ca. 60%) but the reaction is accompanied by the formation of elemental selenium. A comparable yield is achieved by use of an aza transfer reagent (55-70%) (equation 54). The best yield and purest material are obtained from the... 

Amino-l,3,4-selenadiazoles (179) were prepared by Lalezari and Shafiee from selenosemicarbazide, a carboxylic acid and phosphorus oxychloride. The initially formed 2-acylamino derivatives (178) were hydrolyzed to their corresponding 2-amino compounds [Eq. (47)]. 

Indolin-2-on-5-yl)-l,3,4-selenadiazin-2-ones (213) have been tested as cardiotonic drugs they are prepared by the cyclocondensation of indolinones (212) with selenosemicarbazide (Equation... 

Other compounds in this group, viz. 3-alkyl-2,3-dihydro-6//-l, 3,4-selenadiazines (215), are useful as spasmolytic agents. They can be synthesized by the cyclocondensation of 2-halogenoalkanones with selenosemicarbazides (214) (Equation (50)) <90EGP281582,9lCZ36i>. 

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