Round Bottom Flask with two necks

Round Bottom Flask with Two Necks

I've run countless reactions in these flasks, and honestly, they're workhorses you'll reach for daily. Having two necks changes everything—you can drop in reagents through one neck while monitoring temperature or maintaining inert atmosphere through the other. Game-changer for anyone doing serious synthesis work.

Dual-Neck Configuration for Enhanced Reaction Control

Borosilicate 3.3 glass construction handles thermal shock like a champ, cycling from -70°C to +500°C without cracking. I've had flasks survive years of heating, cooling, and vacuum work.

The spherical design distributes heat evenly—no hot spots that could decompose sensitive compounds. When you need more connection points, check out the Round Bottom Flask with three necks or the Round Bottom Flask with three necks, vertical sockets for complex multi-component setups.

Simultaneous Addition and Monitoring Capabilities

• One neck for reagent addition: Connect a dropping funnel or septum for controlled dosing
• Second neck for monitoring: Insert thermometer, gas inlet tube, or pressure equalization adapter
• Inert atmosphere reactions: Maintain nitrogen or argon flow while adding reagents—critical for air-sensitive chemistry
• Stirring operations: Run magnetic stirrer bars while keeping both necks functional

Compatible Joint Sizes and Adapter Options

Standard ground glass joints come in 14/20, 19/26, and 24/29 sizes—precision-ground for leak-proof seals. I keep multiple sizes stocked because you'll need flexibility when connecting condensers, Dean-Stark traps, or addition funnels.

For filtration after reactions, transfer contents using a Filter funnel with glass disc. If you're working with vacuum applications, the Buchner Flask with socket pairs perfectly for downstream processing. The Flask pear shape offers an alternative geometry when you need better draining characteristics.

Distillation and Reflux Setup Applications

Reflux reactions are where these flasks shine. Attach a condenser to one neck, thermometer to the other—you've got complete control. Available from 25mL to 2000mL volumes, so scale from screening reactions to preparative work.

For vacuum distillations, connect your vacuum adapter and fraction collector while maintaining temperature monitoring. The uniform wall thickness (typically 1.8-2.5mm depending on size) ensures consistent heat transfer from your heating mantle. Pro tip: Always use a stirrer bar to prevent bumping during distillations—saves product and prevents dangerous pressure buildups.