3D‐Printing inside the Glovebox: A Versatile Tool for Inert‐Gas Chemistry Combined with Spectroscopy

3D‐Printing with the well‐established ‘Fused Deposition Modeling’ technology was used to print totally gas‐tight reaction vessels, combined with printed cuvettes, inside the inert‐gas atmosphere of a glovebox. During pauses of the print, the reaction flasks out of acrylonitrile butadiene styrene were filled with various reactants. After the basic test reactions to proof the oxygen tightness and investigations of the influence of printing within an inert‐gas atmosphere, scope and limitations of the method are presented by syntheses of new compounds with highly reactive reagents, such as trimethylaluminium, and reaction monitoring via UV/VIS, IR, and NMR spectroscopy. The applicable temperature range, the choice of solvents, the reaction times, and the analytical methods have been investigated in detail. A set of reaction flasks is presented, which allow routine inert‐gas syntheses and combined spectroscopy without modifications of the glovebox, the 3D‐printer, or the spectrometers. Overall, this demonstrates the potential of 3D‐printed reaction cuvettes to become a complementary standard method in inert‐gas chemistry.

1. 3D-printing The UP Plus 2 3D-printer from TierTime Technology Co. Ltd. (PP3DP) was used for all prints without modifications. The printer fits into the standard vacuum chamber of common glove boxes (39 cm diameter) and was evacuated together with all necessary equipment for 1 night before insertion into the glove box. The printing platforms were pasted with ScotchBlue tape (3M) before every print outside the glove box and several platforms kept on stock inside the box. To enable the USB communication with the printer without additional cable connections leading into the glove box, the USB signal was transmitted via ethernet and the ethernet connection was realized by PowerLAN. Outside of the Box the ethernet signal was converted by a standard PowerLAN adapter connected to the power supply of the glove box for the balance and other electronic devices inside the glove box. Inside the glove box the ethernet signal was converted back by a second PowerLAN adapter and passed to an USB over Ethernet Server (UE204, B&B Electronics) which allowed the connection of the 3D-printer. UP! Software 2.13 was used for all prints. The platform was levelled before each print and preheated for 15 min. Printing was performed with a layer height of 0.15 mm and "fine" printing settings. Deviating from the standard parameters, a hatch width of 0.32, hatch speed of 30, jump speed of 50 and hatch scale of 1.0 was set to obtain solid walls. [1] These parameters are only valid for a wall thickness of ~ 3 mm and changes may be necessary for other structures and wall thicknesses. Flasks F3, F5 and F7 printed at air were printed with standard printing settings. Nozzle temperature and all other parameters remained unchanged. Printing was paused shortly and the platform moved to the front to insert solvents and reagents and the stopping time kept as short as possible (few seconds). Printing was continued and if necessary further stops for the addition of subsequent reagents conducted. After completion of the print, a slow cooling down procedure was performed by cooling down for 10 K and heating up for 5 K until a platform temperature of 50 °C was reached. Reaction vessels were discharged from the box and checked for irregularities. Caution has to be taken in all cases with pyrophoric substances and flammable solvents before heating the reaction vessels. Extreme careful control of printed NMR spinner/tube-combinations should be performed to ensure correct fitting inside the NMR.
Heating was performed in a heating bath of aluminium beads (Lab Armor) to prevent contamination of printed cuvettes. Reaction vessels were opened with a saw after completion of the reaction. Pressure equalization was hearably noticeable during opening of the reaction vessels for some reactions with trimethylaluminium. 3D-models of all reaction vessels and cuvettes were constructed with SketchUP Make 15.3.330. Models were checked and repaired with Netfabb basic 5.2.1.
The 3D-printing materials ABS (natural, ABS-N), ABS (clear, ABS-K) and smartABS (natural) were bought as 1.75 mm filaments from Orbi-Tech GmbH, Leichlingen and dried over night at 60 °C and left one night in the vacuum chamber before insertion into the glove box.

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The soluble fraction of the polymers has been isolated as follows. ABS-N (3.00 g) and ABS-K (3.00 g) have been weighed in separately and dissolved in acetone overnight. After centrifugation for 24 h (4500 U min -1 ) the supernatant solution has been filtered through a 0.45 µm syringe filter. The solvent has been removed in vacuo and the clear residue dried for 5 days at high vacuum. The soluble residue was determined to: Test specimens for tensile testing have been dimensioned according to EN ISO 527-2 (type 1BB, 30×4×2 mm) as well as small stripes (30×10×3 mm). After printing each set of samples (longest side orthogonal to the printing platform and shortest side parallel to the moving direction of the printing platform) out of ABS-N (3 samples per type) inside the glove box and outside (at normal air) with the printing settings for solid walls as mentioned above (and a pause of 6 s between the layers for the specimen 1BB) tensile tests have been performed.     Following the general procedure (flask F6) triphenylmethanol (102 mg, 0.4 mmol) and p-fluorobenzoic acid (3 mg, 6 mol-%) were treated with TMA solution (5.645 g, 2.0 mmol). The initial IR spectrum showed the absence of any OH signals. The crude product was purified by column chromatography (PE:EE, 2:1 v/v, R f =0.84) and after removal of the solvent 1,1,1-triphenylethane (3a) was obtained as white solid. [2,3] Yield: 69 mg (69 %).

Reaction of 1-adamantol (2c)
Following the general procedure (flask F2) 1-adamantol (63 mg, 0.4 mmol) and p-fluorobenzoic acid (3 mg, 5 mol-%) were treated with TMA solution (6.351 g, 2.3 mmol). The crude product was recrystallized from dry chloroform to yield [Me 2 Al(µ-O-adamantyl)] 2 (3c) as a white powder. 6 Yield: 57 mg (33 %). The reaction flask F8 combined with an NMR-tube was printed with natural ABS-N. Stock solutions of dry cyclohexanone (101 mg, 1.0 mmol) in dry d18-octane (1.311 g) and of distilled trimethylsilyl chloride (TMSCl) (198 mg, 1.8 mmol) in d18-octane (1.362 g) were prepared separately. The TMSCl stock solution (845 mg, 1.0 mmol, 1.6 eq.) was mixed with the cyclohexanone stock solution (857 mg, 0.6 mmol). The combined clear solution was inserted to flask F8 via a syringe during a first pause of the print. Dry triethylamine (131 mg, 1.3 mmol, 2.0 eq.) was added via a microsyringe during a second pause of the print. After finishing the print, flask F8 was discharged from the glove box and carefully checked for irregularities. Initial NMR-spectra ( 13 C, 29 Si) were recorded directly after discharging and flask F8 was heated upside down at 85 °C in a aluminum bead bath. The flask was cooled down for the repeated measurement of NMR-spectra and heating continued after each measurement.
No indication of enolisation was noticeable in the NMR-spectra. Figure S11: 13 C-NMR-spectra of the enolisation of cyclohexanone with TMSBr directly after discharging flask F8 from the glove box (bottom) and after 120, 210 and 300 min (top) at 85 °C. Figure S12: 29 Si-NMR-spectra of the enolisation of cyclohexanone with TMSBr directly after discharging flask F8 from the glove box (bottom) and after 300 min (top) at 85 °C.

Polystyrene P1
Following the general procedure, CuBr (23 mg, 0.16 mmol) and dnnbipy (143 mg, 0.35 mmol) were used as catalyst. Dbib (10 mg, 0.03 mmol) as initiator was mixed with the styrene stock solution (15.799 g, 17.0 mmol styrene) and added to the catalyst. After 21 h at 85 °C the polymer was precipitated as white powder.

Polystyrene P2
Following the general procedure, CuBr (27 mg, 0.19 mmol) and dnnbipy (142 mg, 0.35 mmol) were used as catalyst. Dbib (10 mg, 0.03 mmol) as initiator was mixed with the styrene stock solution (15.323 g, 16.5 mmol styrene) and added to the catalyst. After 56 h at 85 °C the polymer was precipitated as white powder.