rac-2,3-Dibromopropionamide

The racemic title compound, C3H5Br2NO, was crystallized from methanol. In the crystal, adjacent molecules are linked through N—H⋯O hydrogen bonds, forming chains along the c-axis direction. These chains are linked through N—H⋯O hydrogen bonds, forming an undulating two-dimensional network lying parallel to the bc plane. There are also short Br⋯Br contacts present [3.514 (3) Å].


Crystal data
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BG2488). The discovery of AA in food was, and still is, a matter of public concern, due to its neurotoxic, clastogenic and probably carcinogenic effects. For the determination of AA various sample handling techniques such as defatting, liquid-liquid extraction, solid-phase extraction using different types of cartridges were applied followed either by high-performance liquid chromatography (HPLC) with mass spectrometric (MS) or diode array detection (DAD) or by gas chromatography (GC) with electron-capture (ECD) or MS detection.
When using GC-MS, AA can be analysed without derivatization but is normally brominated to form a derivative revealing improved GC properties (more volatile and less polar). A conversion of AA to 2,3-dibromopropionamide (2,3-DBPA) is usually performed by addition of anhydrous potassium bromide, hydrobromic acid and a saturated solution of bromine in water (protocol by Hashimoto, 1976) or by using KBr-KBrO 3 to avoid elemental bromine (Nemoto et al., 2002). The resulting 2,3-DBPA is extracted from aqueous solutions and can be more easily detected with GC-ECD/MS. However, different studies have shown that under certain conditions, 2,3-DBPA can be decomposed to the more stable derivative 2-bromopropenamide (2-BPA) during GC-analysis. Therefore, triethylamine is meanwhile used to convert 2,3-DBPA to the stable 2-BPA in a second derivatization step prior to GC analysis. The compound crystallizes in the monoclinic space group P2 1 /c. The molecular structure of the compound and the atom-labeling scheme are displayed in  Fig. 2). Between two of the bromine atoms a type I halogene interactions can be observed (Pedireddim et al., 1994). These halogen···halogen contacts C-X···X-C are defined as type I if the C-X···X angle α1 is equal or nearly equal to the X···X-C angle α2. Type I contacts arise as a result of close packing about an inversion center.

Experimental
A 250 mL three-necked round-bottomed flask fitted with a thermometer, a magnetic stirrer, a condenser and a 100 mL dropping funnel, was charged with 60 mL chloroform followed by 5 g (70.33 mmol) of acrylamide. The solution was cooled to 0-5°C in an ice bath, and bromine (11.24 g, 70.33 mmol) dissolved in 20 mL chloroform was added cautiously repeated recrystallization it was not possible to completely avoid builtups degradation products. Therfore, larger crystals were chosen for X-ray single-crystal structure analysis to reduce the influence of buitups on the crystal surface.

Refinement
Decomposition of the crystals during the measurments was observed, but repeated measurements using different crystals did not lead to a better dataset. All H-atoms were positioned geometrically and refined using a riding model with d(C-H) = 0.93 Å, U iso =1.2U eq (C) for aromatic 0.98 Å, U iso = 1.2U eq (C) for CH, 0.97 Å, U iso = 1.2U eq (C) for CH 2 , 0.96 Å, and 0.82 Å, U iso = 1.5U eq (N) for the amino group.

Computing details
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.